[rs6000] Add compatible implementations of x86 SSSE3 intrinsics

[rs6000] Add compatible implementations of x86 SSSE3 intrinsics

This is a follow-on to earlier commits for adding compatibility
implementations of x86 intrinsics for PPC64LE.  This is the first of
two patches.  This patch adds the 32 x86 intrinsics from
<tmmintrin.h> ("SSSE3").  (Patch 2/2 adds tests for these intrinsics,
and briefly describes the tests performed.)

gcc/ChangeLog:

2018-10-26  Paul A. Clarke  <pc@us.ibm.com>

	* config/rs6000/tmmintrin.h: New file.
	* config.gcc (powerpc*-*-*): Add tmmintrin.h to extra_headers.

From-SVN: r265542