Building pthreads inline with gcc and enable optional posix threads in libgcc

[tonytheodore]

Firstly, build pthreads inline and enable libgomp:

• fixes "~winpthreads changes ~pthread_signal.h" etc. reported by build-pkg.
  mingw-w64 installs dummy headers if winpthreads isn't built
• enables libgomp to avoid double-build (see openmp #331)
• no change in openmp-validation (still 20 failures - taken with a grain of
  salt as the batch file test runner isn't a reliable perl substitute)
• pthreads virtual package kept for future testing

Then enbale MXE_GCC_THREADS and allow target spec <triplet>.<link>.<threads>:

• enables optional c++11 <thread>, <mutex>, and <future> in libgcc
• avoid double build advice for posix threads
• not heavily tested but should be released for feedback

Current builds will continue to use the win32 threading default, to enable posix threads:

make MXE_TARGETS=i686-w64-mingw32.static.posix

[tonytheodore]

See the Qt wiki and stack overflow question for some discussion on threading.

Maybe we should do the exception variants at the same time?

[starius]

Thank you! Let me build all packages to make sure that nothing was broken.

Maybe we should do the exception variants at the same time?

These changes seem to be unrelated.

[tonytheodore]

Let me build all packages to make sure that nothing was broken.

Thanks, I saw some issues with cegui, ffmpeg, and opencsg but can't replicate them - seem to be affected by some other package being built earlier.

Maybe we should do the exception variants at the same time?

These changes seem to be unrelated.

Agreed, enabling them isn't hard but we have no way of testing every combination. It's also not yet clear if threads should be options or defaults.

[starius]

opencv is broken

[starius]

The build is completed.
grep build-pkg log > https://gist.github.com/starius/01db21c22331a2701f7c
Only opencv and cimg (which depends on opencv) are broken.

[tonytheodore]

opencv is broken

It was missing the mingww-64 patch.

[starius]

Let me build all packages again.

[starius]

All packages were built successfully.

[tonytheodore]

Thanks! I'll merge this for now so we can start experimenting with target specs.