Add LLVM_FALLTHROUGH annotation after switch
Add LLVM_FALLTHROUGH annotation after switch

This silences a -Wimplicit-fallthrough warning from clang. GCC does not
appear to warn when the case body ends in a switch.

This is a somewhat surprising but intended fallthrough that I pulled out
from my mechanical patch. The code intends to handle 'Yi' and related
constraints as the 'x' constraint.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@345873 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang