This adds code to protect WebAssembly's `trunc_s` family of opcodes
from values outside their domain. Even though such conversions have
full undefined behavior in C/C++, LLVM IR's `fptosi` and `fptoui` do
not, and only return undef.

This also implements the proposed non-trapping float-to-int conversion
feature and uses that instead when available.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@319128 91177308-0d34-0410-b5e6-96231b3b80d8

To fully avoid trapping on wasm, fptoui needs a second check to ensure that
the operand isn't below the supported range.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@319354 91177308-0d34-0410-b5e6-96231b3b80d8