Fix Linux CentOS buildbot handing on ffmpeg test

Don't use -ffast-math functions for libc compatibility implementation, since
then the function ends up calling itself. This may not be ideal for performance
but should be insignificant in practice.

intern/libc_compat/CMakeLists.txt

@@ -32,6 +32,4 @@ set(SRC
 set(LIB
 )
 
-add_c_flag(-ffast-math)
-
 blender_add_lib(bf_intern_libc_compat "${SRC}" "${INC}" "${INC_SYS}" "${LIB}")