Revert "cmake: Require that compiler support keyword '__thread'"
Revert "cmake: Require that compiler support keyword '__thread'"

This reverts commit e2cbb8648aeee9856b7897f9fa06bdd771c39ec0.

The reverted patch, if you used clang, effectively made clang>=3.2
or non-ancient gcc a requirement.

XCode 3.1 ships with an old version of gcc that does not support TLS.
There are Waffle users that require support for XCode 3.1.

Tested on Mac OS with XCode 3.1 gcc and XCode 4.6.2 clang by Nigel.

Tested-by: Nigel Stewart <ab02c6caead0f3530a28ee6ec7b0d1c00356e99e@gmail.com>
Signed-off-by: Chad Versace <a557f7f75bf28dc19ac99107f5cc7cd6b3fbdb1a@linux.intel.com>

maurossi/waffle,janesma/waffle,dcbaker/waffle,chadversary/waffle,waffle-gl/waffle,yinquan529/waffle-gl-waffle,maurossi/waffle,waffle-gl/waffle,janesma/waffle,fjhenigman/waffle,waffle-gl/waffle,evelikov/waffle,yinquan529/waffle-gl-waffle,dcbaker/waffle,janesma/waffle,yinquan529/waffle-gl-waffle,maurossi/waffle,evelikov/waffle,chadversary/waffle,dcbaker/waffle,chadversary/waffle,fjhenigman/waffle,evelikov/waffle,waffle-gl/waffle,fjhenigman/waffle