Support stacktrace on Windows

adds 'strace_win' CONFIG option
Fixes: 1) Building fails w/o  "CONFIG += strace_win" 2) mingw build

Commenting Mingw release flags section for now. Strace is not reliable with mingw (only calls to other libraries are resolved, internal calls show up as addresses).
Merge pull request #337 from Gelmir/stacktrace_win

Support stacktrace on Windows