[PowerPC] Fix PR22711 - Misaligned .toc section

Straightforward patch to emit an alignment directive when emitting a
TOC entry.  The test case was generated from the test in PR22711 that
demonstrated a misaligned .toc section.  The object code is run
through llvm-readobj to verify that the correct alignment has been
applied to the .toc section.

Thanks to Ulrich Weigand for running down where the fix was needed.

llvm-svn: 230801