Replace incorrect usage of isInvalidDecl with intended setInvalidDecl 
Replace incorrect usage of isInvalidDecl with intended setInvalidDecl 

This typo would cause an attempt to multiversion 'main' to issue an
error, but not mark the function as invalid.  This patch fixes it.



git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@325716 91177308-0d34-0410-b5e6-96231b3b80d8

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