AArch64: simplify PCS mapping.

Now that LLVM can count the registers needed to implement AAPCS rules, we don't
need to duplicate that logic here. This means we can drop the explicit padding
and also use more natural types in many cases (e.g. "struct { float arr[3]; }"
used to end up as "[2 x double]" to avoid holes on the stack.

The one wrinkle is that AAPCS va_arg was also using the register counting
machinery. But the local replacement isn't too bad.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@222904 91177308-0d34-0410-b5e6-96231b3b80d8
Create a new 'flag_enum' attribute.

This attribute serves as a hint to improve warnings about the ranges of
enumerators used as flag types. It currently has no working C++ implementation
due to different semantics for enums in C++. For more explanation, see the docs
and testcases.

Reviewed by Aaron Ballman.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@222906 91177308-0d34-0410-b5e6-96231b3b80d8
[OPENMP] Additional processing of 'omp atomic write' directive.
According to OpenMP standard, Section 2.12.6, atomic Construct, '#pragma omp atomic write' is allowed to be used only for expression statements of form 'x = expr;', where x is a lvalue expression and expr is an expression with scalar type. Patch adds checks for it.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@222913 91177308-0d34-0410-b5e6-96231b3b80d8