[rs6000] Add tests for compatible implementations of x86 SSSE3 intrinsics

[rs6000] Add tests for compatible implementations of x86 SSSE3 intrinsics

This is part 2/2 for contributing PPC64LE support for X86 SSSE3 instrisics.
This patch includes testsuite/gcc.target tests, copied from gcc.target/i386,
for the intrinsics defined in tmmintrin.h.

[gcc/testsuite]

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

	* gcc.target/powerpc/ssse3-check.h: New file.
	* gcc.target/powerpc/ssse3-vals.h: New file.
	* gcc.target/powerpc/ssse3-pabsb.c: New file.
	* gcc.target/powerpc/ssse3-pabsd.c: New file.
	* gcc.target/powerpc/ssse3-pabsw.c: New file.
	* gcc.target/powerpc/ssse3-palignr.c: New file.
	* gcc.target/powerpc/ssse3-phaddd.c: New file.
	* gcc.target/powerpc/ssse3-phaddsw.c: New file.
	* gcc.target/powerpc/ssse3-phaddw.c: New file.
	* gcc.target/powerpc/ssse3-phsubd.c: New file.
	* gcc.target/powerpc/ssse3-phsubsw.c: New file.
	* gcc.target/powerpc/ssse3-phsubw.c: New file.
	* gcc.target/powerpc/ssse3-pmaddubsw.c: New file.
	* gcc.target/powerpc/ssse3-pmulhrsw.c: New file.
	* gcc.target/powerpc/ssse3-pshufb.c: New file.
	* gcc.target/powerpc/ssse3-psignb.c: New file.
	* gcc.target/powerpc/ssse3-psignd.c: New file.
	* gcc.target/powerpc/ssse3-psignw.c: New file.

From-SVN: r265544