clang/test/Sema/struct-packed-align.c: Add the case in MS mode that alignment...

clang/test/Sema/struct-packed-align.c: Add the case in MS mode that alignment doesn't affect packing.

Also, revert a couple of suppressions.
  r214298, "Suppress clang/test/Sema/struct-packed-align.c for targeting LLP64."
  r214301, "Suppress clang/test/Sema/struct-packed-align.c also on msvc for investigating."

llvm-svn: 214794