CMake: Kits do not get updated when environment changes

Steps to reproduce:

• have predefined kits, toolchains,... for QC, do not have CMake provided by Visual Studio
• open the toolchains.xml and remove all tags (including its children) with the key ProjectExplorer.MsvcToolChain.environmentModifications
• open QC again with these settings
  • check the kits options page - all of the kits have warnings regarding there's no compiler set although the kit has a correct one set
• open a cmake based project
• try to build it

Current result:

• cl cannot be found in PATH

Expected result:

• environment modifications are propagated to the build system as well

Note: Restarting QC (the environmentModifications sections have been rewritten with the former start) solves the problem, as now the PATH variable has been set to cl as well.

Side note: we're using this approach for testing and we have only a stripped down set of data inside the config files to be more generic when it comes to different machines. These settings used to work up to QC 4.9, so I'd say this is a regression.

Found by Squish test tst_cmake_speedcrunch.