Fwiw, the failing tests with clang:

```
>>>>> processing /Users/runner/work/octave/octave/.build/libinterp/corefcn/mappers.cc-tst
***** test
rval = pi/2;
ival = 1.31695789692481635;
obs = asin ([2, 2-i*eps, 2+i*eps]);
exp = [rval - ival*i, rval - ival*i, rval + ival*i];
assert (obs, exp, 2*eps);
obs = asin ([-2, -2-i*eps, -2+i*eps]);
exp = [-rval + ival*i, -rval - ival*i, -rval + ival*i];
assert (obs, exp, 2*eps);
assert (asin ([2 0]), [rval - ival*i, 0], 2*eps);
assert (asin ([2 0i]), [rval - ival*i, 0], 2*eps);
!!!!! test failed
ASSERT errors for: assert (obs,exp,2 * eps)
Location | Observed | Expected | Reason
(3) 1.5708+1.317i 1.5708+1.317i Abs err 1.1102e-15 exceeds tol 4.4409e-16 by 7e-16
shared variables scalar structure containing the fields:
rt2 = 1.4142
rt3 = 1.7321
>>>>> processing /Users/runner/work/octave/octave/scripts/general/logspace.m
***** assert (logspace (Inf + 1i, Inf + 1i, 3), repmat (complex (-Inf,Inf), [1, 3]))
!!!!! test failed
ASSERT errors for: assert (logspace (Inf + 1i, Inf + 1i, 3),repmat (complex (-Inf, Inf), [1, 3]))
Location | Observed | Expected | Reason
(1) Inf+NaNi -Inf+Infi 'NaN' mismatch
(2) Inf+NaNi -Inf+Infi 'NaN' mismatch
(3) Inf+NaNi -Inf+Infi 'NaN' mismatch
***** assert (logspace (-Inf + 1i, Inf + 1i, 3), [0, NaN + NaN * 1i, complex(-Inf, Inf)])
!!!!! test failed
ASSERT errors for: assert (logspace (-Inf + 1i, Inf + 1i, 3),[0, NaN + NaN * 1i, complex(-Inf, Inf)])
Location | Observed | Expected | Reason
(3) Inf+NaNi -Inf+Infi 'NaN' mismatch
>>>>> processing /Users/runner/work/octave/octave/scripts/miscellaneous/memory.m
***** testif ; isunix () || ispc ()
[user, syst] = memory ();
assert (user.mem_used_octave > 0);
assert (user.ram_used_octave <= user.mem_used_octave);
assert (user.mem_used_octave < syst.SystemMemory.Total);
assert (user.MemAvailableAllArrays <= syst.SystemMemory.Available);
!!!!! test failed
textscan: invalid stream number = -1
>>>>> processing /Users/runner/work/octave/octave/scripts/plot/util/hgsave.m
***** testif HAVE_MAGICK; (have_window_system () && __have_feature__ ("QT_OFFSCREEN") && strcmp ("qt", graphics_toolkit ())) || strcmp ("gnuplot", graphics_toolkit ());
h1 = figure ("visible", "off", "paperposition", [0.25, 2.5, 8.0, 6.0]);
unwind_protect
x = 0:0.1:2*pi;
y1 = sin (x);
y2 = exp (x - 1);
ax = plotyy (x,y1, x-1,y2, @plot, @semilogy);
xlabel ("X");
ylabel (ax(1), "Axis 1");
ylabel (ax(2), "Axis 2");
axes (ax(1));
text (0.5, 0.5, "Left Axis", ...
"color", [0 0 1], "horizontalalignment", "center");
axes (ax(2));
text (4.5, 80, "Right Axis", ...
"color", [0 0.5 0], "horizontalalignment", "center");
ftmp = [tempname() ".ofig"];
png1 = [tempname() ".png"];
png2 = [tempname() ".png"];
unwind_protect
hgsave (h1, ftmp);
print (h1, png1);
[img1, map1, alpha1] = imread (png1);
h2 = hgload (ftmp);
print (h2, png2);
[img2, map2, alpha2] = imread (png2);
unwind_protect_cleanup
unlink (ftmp);
unlink (png1);
unlink (png2);
end_unwind_protect
assert (img1, img2);
assert (map1, map2);
assert (alpha1, alpha2);
unwind_protect_cleanup
close (h1);
close (h2);
end_unwind_protect
!!!!! test failed
ASSERT errors for: assert (img1,img2)
Location | Observed | Expected | Reason
(58,1097,1) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1098,1) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1100,1) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1101,1) 206 233 Abs err 27 exceeds tol 0 by 3e+01
(58,1102,1) 206 216 Abs err 10 exceeds tol 0 by 1e+01
(58,1103,1) 206 240 Abs err 34 exceeds tol 0 by 3e+01
(58,1104,1) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1105,1) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1106,1) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1107,1) 206 254 Abs err 48 exceeds tol 0 by 5e+01
(58,1108,1) 255 219 Abs err 36 exceeds tol 0 by 4e+01
(58,1109,1) 255 219 Abs err 36 exceeds tol 0 by 4e+01
(58,1113,1) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1114,1) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1115,1) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1118,1) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1119,1) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1120,1) 206 246 Abs err 40 exceeds tol 0 by 4e+01
(58,1121,1) 255 216 Abs err 39 exceeds tol 0 by 4e+01
(58,1122,1) 206 253 Abs err 47 exceeds tol 0 by 5e+01
(58,1123,1) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1124,1) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1127,1) 206 253 Abs err 47 exceeds tol 0 by 5e+01
(58,1128,1) 206 246 Abs err 40 exceeds tol 0 by 4e+01
(58,1097,2) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1098,2) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1100,2) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1101,2) 206 155 Abs err 51 exceeds tol 0 by 5e+01
(58,1102,2) 206 82 Abs err 124 exceeds tol 0 by 1e+02
(58,1103,2) 206 190 Abs err 16 exceeds tol 0 by 2e+01
(58,1104,2) 67 255 Abs err 188 exceeds tol 0 by 2e+02
(58,1105,2) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1106,2) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1107,2) 206 252 Abs err 46 exceeds tol 0 by 5e+01
(58,1108,2) 255 94 Abs err 161 exceeds tol 0 by 2e+02
(58,1109,2) 255 97 Abs err 158 exceeds tol 0 by 2e+02
(58,1110,2) 255 254 Abs err 1 exceeds tol 0 by 1
(58,1113,2) 67 255 Abs err 188 exceeds tol 0 by 2e+02
(58,1114,2) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1115,2) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1118,2) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1119,2) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1120,2) 206 215 Abs err 9 exceeds tol 0 by 9
(58,1121,2) 255 82 Abs err 173 exceeds tol 0 by 2e+02
(58,1122,2) 67 248 Abs err 181 exceeds tol 0 by 2e+02
(58,1123,2) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1124,2) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1127,2) 206 244 Abs err 38 exceeds tol 0 by 4e+01
(58,1128,2) 206 214 Abs err 8 exceeds tol 0 by 8
(58,1097,3) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1098,3) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1100,3) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1101,3) 206 122 Abs err 84 exceeds tol 0 by 8e+01
(58,1102,3) 206 24 Abs err 182 exceeds tol 0 by 2e+02
(58,1103,3) 206 168 Abs err 38 exceeds tol 0 by 4e+01
(58,1104,3) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1105,3) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1106,3) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1107,3) 206 251 Abs err 45 exceeds tol 0 by 4e+01
(58,1108,3) 255 40 Abs err 215 exceeds tol 0 by 2e+02
(58,1109,3) 255 44 Abs err 211 exceeds tol 0 by 2e+02
(58,1110,3) 255 253 Abs err 2 exceeds tol 0 by 2
(58,1113,3) 67 255 Abs err 188 exceeds tol 0 by 2e+02
(58,1114,3) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1115,3) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1118,3) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1119,3) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1120,3) 206 202 Abs err 4 exceeds tol 0 by 4
(58,1121,3) 255 24 Abs err 231 exceeds tol 0 by 2e+02
(58,1122,3) 67 245 Abs err 178 exceeds tol 0 by 2e+02
(58,1123,3) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1124,3) 206 255 Abs err 49 exceeds tol 0 by 5e+01
(58,1127,3) 206 241 Abs err 35 exceeds tol 0 by 4e+01
(58,1128,3) 206 200 Abs err 6 exceeds tol 0 by 6
>>>>> processing /Users/runner/work/octave/octave/test/mex/bug-51725.tst
***** assert (bug_51725 (), [])
!!!!! test failed
'bug_51725' undefined near line 2, column 2
***** error <element number 2 undefined in return list> [x,y,z] = bug_51725 ();
!!!!! error failed.
Expected <element number 2 undefined in return list>, but got <'bug_51725' undefined near line 2, column 2>
>>>>> processing /Users/runner/work/octave/octave/test/mex/bug-54096.tst
***** test
s = bug_54096 ();
assert (s, struct ("field", []));
assert (s.field, []);
!!!!! test failed
'bug_54096' undefined near line 3, column 3
>>>>> processing /Users/runner/work/octave/octave/test/mex/mexnumtst.tst
***** test
s = rand (3, 4, "single");
sc = s + i * rand (3, 4, "single");
d = rand (3, 4, "double");
dc = d + i * rand (3, 4, "double");
[sx, scx, dx, dcx] = mexnumtst (s, sc, d, dc);
assert (s, sx)
assert (sc, scx)
assert (d, dx)
assert (dc, dcx)
!!!!! test failed
'mexnumtst' undefined near line 8, column 8
>>>>> processing /Users/runner/work/octave/octave/scripts/specfun/expint.m
***** test <*47738>
assert (expint (10i), 0.0454564330044554 + 0.0875512674239774i, -4*eps);
!!!!! regression: https://octave.org/testfailure/?47738
ASSERT errors for: assert (expint (10i),0.0454564330044554 + 0.0875512674239774i,-4 * eps)
Location | Observed | Expected | Reason
() 0.045456+0.087551i 0.045456+0.087551i Rel err 9.1442e-16 exceeds tol 8.8818e-16 by 3e-17
```

I’m not sure if all of those are due to the different standard library implementations.