Resource-manager.h includes <Qsci/qscilexer.h> unconditionally

I ma trying to compile 7.0.1 w/o qscintilla. Configure correctly tells me that qscintilla is not found, but make fails with:

libtool: compile:  clang++ -DHAVE_CONFIG_H -I. -I.. -I/usr/include/qt5/QtCore -I/usr/include/qt5 -I/usr/include/qt5/QtGui -I/usr/include/qt5/QtHelp -I/usr/include/qt5/QtWidgets -I/usr/include/qt5/QtSql -I/usr/include/qt5/QtNetwork -I/usr/include/qt5/QtPrintSupport -I/usr/include/qt5/QtXml -I../libgui/qterminal/libqterminal -I../libgui/src -Iliboctave -I../liboctave/array -Iliboctave/numeric -I../liboctave/numeric -Iliboctave/operators -I../liboctave/operators -I../liboctave/system -I../liboctave/util -Ilibinterp -I../libinterp -Ilibinterp/parse-tree -I../libinterp/parse-tree -Ilibinterp/corefcn -I../libinterp/corefcn -I../libinterp/octave-value -I../liboctave/wrappers -fPIC -pthread -fopenmp -O3 -march=native -mavx -mavx2 -flto=thin -MT libgui/qterminal/libqterminal/la-QTerminal.lo -MD -MP -MF libgui/qterminal/libqterminal/.deps/la-QTerminal.Tpo -c ../libgui/qterminal/libqterminal/QTerminal.cc  -fPIC -DPIC -o libgui/qterminal/libqterminal/.libs/la-QTerminal.o
In file included from ../libgui/qterminal/libqterminal/QTerminal.cc:41:
In file included from ../libgui/src/octave-qobject.h:38:
../libgui/src/resource-manager.h:32:10: fatal error: 'Qsci/qscilexer.h' file not found
#include <Qsci/qscilexer.h>
         ^~~~~~~~~~~~~~~~~~
1 error generated.

That looks like a bug – we should either fail at configure stage or include and use those files conditionally.

I agree that this looks like a bug.
I think we should support building the GUI without QScintilla.
I pushed a patch here that includes that header conditionally on the configure results:
octave: 8d303ace1aff (gnu.org)

@mmuetzel, thanks for fixing this bug I have introduced with my changset bb6bb306b8a6.