Easily configurable system header locations on Windows.

[mheinsen]

Clang has different methods for finding system headers based on the environment used on Windows (e.g. mingw, msys, visual studio). At least for the case that we usually test with (mingw), we require PATH to be set correctly also (i.e. gcc.exe must be in the path, and the headers must be in the correct location relative to gcc.exe's location). Rather than require users to correctly setup their command line environment, and specify the correct target (if they are using something other than our expected default), it would be nice if these options and paths could be configured through the trace viewer's preferences.

[mheinsen]

There is more trouble here than first appears. To use the x86_64-windows-msvc target, SeeC must be updated to work correctly with MSVC's LINK. See #62.

[mheinsen]

This issue was moved to seec-team#18