[libc] Enable fmaf and fma on x86_64.

They require clang-11 or above for building and hence had to be disabled
as the bots did not have clang-11 or higher. Bots have now been upgraded
so we can enable these functions now.

GitOrigin-RevId: b47539a14dc8a40e8710aef2fb75d2486f271dba
1 file changed