fix MinGW compiler detection

We must take the executable suffix into account.

Change-Id: Idcb6abbf7801d2a1d49239ed81521d83a278e4f1
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>
remove property includeDirName from QtModule.qbs

The usage of this property was removed in 04e5834e.

Change-Id: Ib938d9761f432b5b3cfad27d6c4008061edb69c7
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>
remove unused property qtModulePrefix from Qt modules

This was used to calculate include and library names.
That's done in setup-qt now.

Change-Id: Ief2b17e9fdf65e829dc563dac49e70d8dcbaebee
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>