Relax assertion in ReplaceableMetadataImpl::replaceAllUsesWith(). There is a legitimate use-case in clang where we need to replace a temporary placeholder node with the temporary node that may be a forward declaration.
Relax assertion in ReplaceableMetadataImpl::replaceAllUsesWith().
There is a legitimate use-case in clang where we need to replace a
temporary placeholder node with the temporary node that may be a
forward declaration.

<rdar://problem/24493203>

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@259973 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit e56d199eb3bc85d981de5fab1fb82e0ad502575b)

apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm