The vcxproj generator completely ignored QMAKE_CFLAGS and did only read
QMAKE_CXXFLAGS. The msbuild-internal "cl compiler tool" contains the
flags for both, C and C++. It is to risky to take all QMAKE_CFLAGS into
account for the "cl compiler tool", because this might collide with what
is specified in QMAKE_CXXFLAGS. Therefore, we only read the
/std:... compiler option from QMAKE_CFLAGS and set the
LanguageStandard_C flag in the msbuild file.
Pick-to: 6.2 5.15
Task-number: QTBUG-89296
Change-Id: I885061802c1350b293a7868d4c9a9367d30e2380
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>
a6a216e310