[WebAssembly] Add a pass to create wrappers for function bitcasts.
WebAssembly requires caller and callee signatures to match exactly. In LLVM,
there are a variety of circumstances where signatures may be mismatched in
practice, and one can bitcast a function address to another type to call it
as that type. This patch adds a pass which replaces bitcasted function
addresses with wrappers to replace the bitcasts.
This doesn't catch everything, but it does match many common cases.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@291315
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