ffa6f057b4
Support for C11's _Thread_local was introduced in GCC in the 4.9 series, even though we make the C11 compiler flags available in CMake with GCC >= 4.6. FreeBSD's runetype.h uses _Thread_local, which causes CMake's own build to fail when using GCC < 4.9 and -std=gnu11: /usr/include/runetype.h:92:22: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'const' extern _Thread_local const _RuneLocale *_ThreadRuneLocale; Add a test for _Thread_local support and only build CMake itself with C11 support if it works. Bug: http://www.cmake.org/Bug/view.php?id=15741