with 40e87491 merged, 'QMAKE_CXXFLAGS' variable in
'win32-g++' toolchain became defined via 'QMAKE_CFLAGS'.
the similar can be found in 'win32-clang-msvc' and
'win32-icc' toolchains too.
this works for now, because such definitions just duplicates code
from includes, like 'gcc-base.conf', 'msvc-desktop.conf', etc.
but it would became broken, if changes would be applied to
'QMAKE_CXXFLAGS' definitions in that includes, prior
to the redefinitions in 'win32-*/qmake.conf' toolchains.
thus 'QMAKE_CXXFLAGS' definitions in 'win32-*/qmake.conf' toolchains
should not depend on 'QMAKE_CFLAGS' and be done explicitly.
in order to apply this change correctly to 'win32-icc' toolchain,
its 'QMAKE_CFLAGS' variable should become dependent on definitions
in the includes, similar to 'win32-clang-msvc' and
'win32-msvc' toolchains.
Change-Id: I5e820e44a769a590ba63f70dcb3a115311093311
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>
7ff3032b22