The MinGW resource compiler fails to handle compile definitions
with multiple values.
When the resource file is compiled as part of the main target rather
than a separate object library, the resource generation rule will
inherit all the compile definitions from the main target.
For the case of tst_selftests this causes errors like
gcc: error: badxml\: No such file or directory
gcc: error: benchlibcallgrind\: No such file or directory
gcc: error: benchlibcounting\: No such file or directory
gcc: error: benchlibeventcounter\: No such file or directory
gcc: error: benchliboptions\: No such file or directory
Limit the compile definition to the C++ language only, so the multiple
values are not passed to the resource compiler.
Pick-to: 6.2
Change-Id: Ie53666839272556323b50d79c090f0dc71745d11
Reviewed-by: Cristian Adam <cristian.adam@qt.io>
3a19c5b2e6