QT_HASH_SEED does not ensure test stability accross different platforms/compilers/machines due to SSE4.2 support

qHash() implementations for string-like types (QString, QByteArray...) has two different implementations depending on whether the compiler and CPU support SSE 4.2. Each implementation provides different results for the same input, which makes it impossible to ensure unit-tests stability across different machines (developer workstation and CI for example).

qhash.cpp:hasFastCrc32() should either return false if QT_HASH_SEED is set or it should be at least documented that QT_NO_CPU_FEATURE=sse4.2 must be set to ensure identical behaviour across different platforms/compilers/CPUs.