Revert useless part of r217349

Adding handling of __builtin_assume_aligned to IntExprEvaluator does not make
sense because __builtin_assume_aligned returns a pointer (not an integer).
Thanks to Richard for figuring out why this was not doing anything.

I'll add this back in a better place (PointerExprEvaluator perhaps).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@218958 91177308-0d34-0410-b5e6-96231b3b80d8
Make test/Sema/atomic-ops.c free-standing

This test includes stdint.h, which might include system headers (and that might
not work, depending on the system configuration). Attempting to fix
llvm-clang-lld-x86_64-debian-fast.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@218959 91177308-0d34-0410-b5e6-96231b3b80d8