[Linkerwrapper] Make -Xoffload-linker pass directly to clang

Summary:
We provide `-Xoffload-linker` to pass arguments directly to the link
step. Currently this uses `-Wl,` implicitly which prevents us from using
clang options that we otherwise could make use of. This patch removes
that implicit behavior as users can just as easiliy pass
`-Xoffload-linker -Wl,-foo` if needed.

clang/test/Driver/linker-wrapper.c

@@ -123,8 +123,8 @@
 // RUN:   --linker-path=/usr/bin/ld --device-linker=a --device-linker=nvptx64-nvidia-cuda=b -- \
 // RUN:   %t.o -o a.out 2>&1 | FileCheck %s --check-prefix=LINKER-ARGS
 
-// LINKER-ARGS: clang{{.*}}--target=amdgcn-amd-amdhsa{{.*}}-Wl,a
-// LINKER-ARGS: clang{{.*}}--target=nvptx64-nvidia-cuda{{.*}}-Wl,a -Wl,b
+// LINKER-ARGS: clang{{.*}}--target=amdgcn-amd-amdhsa{{.*}}a
+// LINKER-ARGS: clang{{.*}}--target=nvptx64-nvidia-cuda{{.*}}a b
 
 // RUN: not clang-linker-wrapper --dry-run --host-triple=x86_64-unknown-linux-gnu -ldummy \
 // RUN:   --linker-path=/usr/bin/ld --device-linker=a --device-linker=nvptx64-nvidia-cuda=b -- \

clang/tools/clang-linker-wrapper/ClangLinkerWrapper.cpp

@@ -428,7 +428,7 @@ Expected<StringRef> clang(ArrayRef<StringRef> InputFiles, const ArgList &Args) {
         std::back_inserter(CmdArgs));
 
   for (StringRef Arg : Args.getAllArgValues(OPT_linker_arg_EQ))
-    CmdArgs.push_back(Args.MakeArgString("-Wl," + Arg));
+    CmdArgs.push_back(Args.MakeArgString(Arg));
 
   for (StringRef Arg : Args.getAllArgValues(OPT_builtin_bitcode_EQ)) {
     if (llvm::Triple(Arg.split('=').first) == Triple)