Mostly copied from src/gallium/include/pipe/p_config.h, so I kept its
copyright and authorship.
Other than the obvious rename, the big difference is that these are
always defined, to be used as `#if DETECT_OS_LINUX`.
Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Eric Engestrom