Obtain the correct environment in a thread-safe way when appropriate instead.

Fixes Bugzilla #1312.

Thanks to Bill Chenbin for the patch!

We need this for GLES2 support.

Fixes Bugzilla #1290.

Thanks to Gabriel Jacobo for the patch!

--HG--
extra : rebase_source : 80bd6c922b4e9c74582cc85d62462d87431315bd

Fixes Bugzilla #1292.

Thanks to Vittorio Giovara for the patch!

The system headers use them generously.
(transplanted from 825e1072eac6c950ca4f6e879a91ea199a282b2c)

--HG--
extra : transplant_source : %82%5E%10r%EA%C6%C9P%CAOn%87%9A%91%EA%19%9A%28%2B%2C

Fixes Bugzilla #1294.

Thanks to Gabriel Jacobo for the patch!

Thanks to Mako_energy for the fix!

Fixes Bugzilla #1284.

(But probably upsets buildbot.  :)  )

We need the C runtime, which we don't link against, for __try/__except.

--HG--
extra : rebase_source : ae532d4b4d68ef86de0fc2cb6794a622e0841bce

Removed checks for things that are always true, free unneeded struct before
 calling thread entry point, instead of after thread completes.

Favor it over Mac OS X API for Intel systems (but not GCC atomic intrinsics).

This might get us a little further on Cygwin builds, too.