[PATCH 0/3][rs6000] x86-compat vector intrinsics fixes for BE, 32bit

[Paul Clarke]

Many of the tests for the x86-compatible vector intrinsics implementations
were protected by "#ifdef __BUILTIN_CPU_SUPPORTS__", which is only enabled
with recent enough glibc that in most environments, the test were silently
passing without actually testing anything.

Patches which follow:
01: Fix the implementations.
02: Fix the test cases.
03: Enable the tests to actually run the test code.

Bootstrap and regression tested on POWER8 ppc64le, ppc64(be), ppc(32bit be),
and POWER7 ppc64(be).

OK for trunk?

PC