MsvcToolChain: compiler autodetection/selection

The msvc compiler detection could be simplified.
In the end the user should only select the target architecture and compiler version.

Windows SDK 7.1

• ships compilers for x86, amd64, and ia64
• installs the cross-compiler if needed (e.g. x86_amd64 on 32bit system)
• setenv.cmd selects compiler for: x86, x64 (amd64 compiler), ia64
• setenv.cmd automatically selects cross-compiler if needed
• compilers are installed into the same path as Studio 10 (C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\bin)

Studio Express 10

• ships compilers for x86, for other platform the Windows SDK 7.1 is needed
• vcvarsall.bat must be used to explicitely select a compiler (x86, amd64, ia64, x86_amd64, x86_ia64)
• no automatic selection of cross-compiler

Studio Express 11

• ships compilers for x86 and the cross-compiler x86_amd64
• vcvarsall.bat must be used to explicitly select a compiler (x86 or x86_amd64)
• no automatic selection of cross-compiler

Studio Prof 10/11 (someone should check)

• ships compilers for x86, amd64, ia64, arm
• installs the cross-compiler if needed (e.g. x86_amd64 on 32bit system)
• no automatic selection of cross-compiler

The best way to handle this by Creator is to show the user only targets when a compiler
is found (x86, x64, ia64, arm ) and to automatically select the cross-compiler if needed.