To be able to successfully build OpenMP on FreeBSD/i386, which still
uses i486 as its default processor, I had to provide wrappers for the
__kmp_load_mxcsr and __kmp_store_mxcsr functions.
If the compiler signals that SSE is not available, loading and storing
mxcsr does not make sense anway, so in that case the inline functions
are empty. This gives the minimum amount of code churn.