Backport of memmove changes

Backport of memmove changes

This commit merges in the following three origin/master changes into a
single commit.

commit 8ff41c4601f8b8d7dfa6682f596dc4071823424d
Author: Will Schmidt <will_schmidt@vnet.ibm.com>
Date:   Wed Apr 18 16:44:27 2012 -0500

    Have memmove call __builtin_memcopy on PowerPC if src and dest
    don't overlap.

commit 6b652f46c3935088082bb5870b6fd9edbaa92125
Author: Will Schmidt <will_schmidt@vnet.ibm.com>
Date:   Wed Apr 18 15:34:23 2012 -0500

    Further simplify power6 wordcopy by removing switch statements.

    This fix replaces switch statements that contain individual
    [fwd|bwd]_align_merge (<constant>) calls with a single
    [fwd|bwd]_align_merge (align) call.

commit b282631e367f474bbd9e5d92e2aa54b3ce44efe8
Author: Will Schmidt <will_schmidt@vnet.ibm.com>
Date:   Wed Apr 18 14:52:25 2012 -0500

    Simplify power6 wordcopy by adding [fwd|bwd]_align_merge macros.