IRGen: further generalise runtime function generation

This adjusts the runtime function declaration handling to track the
owning module for the well known functions. This allows us to ensure
that we are able to properly identify if the symbol should be imported
or not when building the shared libraries. This will require a
subsequent tweak to allow for checking for static library linkage to
ensure that we do not mark the symbol as DLLImport when doing static
linking.

Author: compnerd

include/swift/Runtime/RuntimeFnWrappersGen.h

@@ -39,7 +39,8 @@ enum class RuntimeAvailability {
 /// given name, return types, argument types, attributes and
 /// a calling convention.
 llvm::Constant *getRuntimeFn(llvm::Module &Module, llvm::Constant *&cache,
-                             char const *name, llvm::CallingConv::ID cc,
+                             const char *ModuleName, char const *FunctionName,
+                             llvm::CallingConv::ID cc,
                              RuntimeAvailability availability,
                              llvm::ArrayRef<llvm::Type *> retTypes,
                              llvm::ArrayRef<llvm::Type *> argTypes,