What is xmmintrin.h, and why aren't ports finding it?

Chris H writes:

>   Working on a recent 11-CURRENT install
>  (11-CURRENT #1 amd64 r274134 Nov 5 12:56:14 PST 2014)
>  svn info /usr/ports Revision: 372176
>  
>  Given the above, and the fact that I have installed lang/gcc-48.
>  Is there any reason that any port wanting to include xmmintrin.h
>  fails to find it? Even though dmesg && messages reflects the fact
>  that gcc48 is included within my $PATH?

	Start by looking at:

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=190669


	Respectfully,


			Robert Huff