[REG 4.1 -> 4.2] Can't parse project qtcreator.qbs

1. Have a kit configured which uses MinGW with g++ 4.9 and Qt 5.4.1. Do not have a C compiler configured explicitly.
2. Have a checkout of Creator's repository at label v4.1.0-beta1.
3. Open the project qtcreator.qbs from that repository in Creator.
4. Configure the project to use the kit from step 1.
   Parsing will fail with the following error message:

   D:\dev\32\MSVC2015\creator-4.2\share\qtcreator\qbs\share\qbs\modules\cpp\GenericGCC.qbs:203: error: The following properties have invalid values:
   cpp.compilerVersion: must be a version number with 3 components
   cpp.compilerVersionMajor: must be an integer >= 1
   cpp.compilerVersionMinor: must be an integer >= 0
   cpp.compilerVersionPatch: must be an integer >= 0
   

When configuring a C compiler for the kit, parsing will succeed. It should still be possible to parse the project without having a C-Compiler configured.

Found by Squish test tst_opencreator_qbs.