[WebAssembly] Define the atomic type sizes
WebAssembly's spec has now been updated to specify some guarantees
about lock free atomic accesses. Update clang to match.
This also updates sig_atomic_t to be 64-bit on wasm64. WebAssembly
does not presently have asynchronous interrupts, but this change is
within the spirit of how they will work if they are added.
Differential Revision: http://reviews.llvm.org/D12862
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@247624
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projects / clang / commit