[libc][NFC] Remove dependence on xmmintrin.h to read/write MXCSR.

The version of clang on the bots is unhappy with using xmmintrin.h.
So, this change removes dependence on xmmintrin by using inline
assembly.

GitOrigin-RevId: 3a375125b01cbb84e90d688f19b0168e2c07862d
1 file changed