introduce cpp.supportedStaticLibrarySuffixes

The MinGW linker supports .a and .lib files as input.
Therefore we need to maintain a list of supported lib suffixes.

Task-number: QBS-376

Change-Id: I2e9c3b424478a9bcf1a06df6e532517b31da0bef
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>