Q_DECL_UNUSED left empty when clang is masquerading as MSVC

When running clang-tidy on a code base that builds with MSVC (cl.exe) qcompilerdetection.h does not define Q_DECL_UNUSED correctly (leaves it defined to nothing). Workaround is to call clang-tidy like:

clang-tidy "-extra-arg=-DQ_DECL_UNUSED=__attribute__((__unused__))" ...

But I don't think this should be necessary.