Can't sensibly test unless the compiler does support raw strings,
since any test that would catch qmake's (prior) inability to parse raw
strings would necessarily confuse the C++ compiler in the same way.
This even applies (in test app code) to any #if-ery around the raw
string, since tokenization happens before preprocessor directives are
resolved.  So the #if-ery on Q_COMPILER_RAW_STRINGS has to be in
tst_qmake.cpp, not the test app it builds.

Change-Id: I4a461f515adff288b54fb273fd9996f9b906d11c
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>