[contrib.glfw3] added support for pthread

[ypujante]

Following some user request, I made the necessary changes to the code as well as the port file to add pthread support. I followed the pattern in other ports (like sdl2) for adding the -pthread option when settings.PTHREAD is defined and used the same extension for the library name (-mt).

[ypujante]

The failing test is the following:

======================================================================
ERROR [0.003s]: test_memorygrowth_linear_step (test_core.wasm64)
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Traceback (most recent call last):
  File "/home/circleci/.pyenv/versions/3.10.7/lib/python3.10/unittest/case.py", lin

[hoodmane]

That seems to be a common flake, I reran the CI for you. Hopefully it won't flake again...

[ypujante]

Thank you. All tests are passing now.