[LinkerWrapper] Fix -Xoffload-linker a=b in offloading (#100270)

Summary:
We have the `-Xoffload-linker=triple=arg` syntax that split the argument
meant only for a single toolchain. However this borke if it was an `a=b`
type argument. Make it only treat it like a triple if it's a valid
triple.

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Differential Revision: https://phabricator.intern.facebook.com/D60250759

Author: jhuber6

clang/test/Driver/linker-wrapper.c

@@ -128,11 +128,12 @@ __attribute__((visibility("protected"), used)) int x;
 // RUN: %clang -cc1 %s -triple x86_64-unknown-linux-gnu -emit-obj -o %t.o \
 // RUN:   -fembed-offload-object=%t.out
 // RUN: clang-linker-wrapper --dry-run --host-triple=x86_64-unknown-linux-gnu \
-// RUN:   --linker-path=/usr/bin/ld --device-linker=a --device-linker=nvptx64-nvidia-cuda=b \
+// RUN:   --linker-path=/usr/bin/ld --device-linker=foo=bar --device-linker=a \
+// RUN:   --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{{.*}}a
-// LINKER-ARGS: clang{{.*}}--target=nvptx64-nvidia-cuda{{.*}}a b
+// LINKER-ARGS: clang{{.*}}--target=amdgcn-amd-amdhsa{{.*}}foo=bar{{.*}}a
+// LINKER-ARGS: clang{{.*}}--target=nvptx64-nvidia-cuda{{.*}}foo=bar{{.*}}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

@@ -1214,7 +1214,13 @@ DerivedArgList getLinkerArgs(ArrayRef<OffloadFile> Input,
   // Forward '-Xoffload-linker' options to the appropriate backend.
   for (StringRef Arg : Args.getAllArgValues(OPT_device_linker_args_EQ)) {
     auto [Triple, Value] = Arg.split('=');
-    if (Value.empty())
+    llvm::Triple TT(Triple);
+    // If this isn't a recognized triple then it's an `arg=value` option.
+    if (TT.getArch() <= Triple::ArchType::UnknownArch ||
+        TT.getArch() > Triple::ArchType::LastArchType)
+      DAL.AddJoinedArg(nullptr, Tbl.getOption(OPT_linker_arg_EQ),
+                       Args.MakeArgString(Arg));
+    else if (Value.empty())
       DAL.AddJoinedArg(nullptr, Tbl.getOption(OPT_linker_arg_EQ),
                        Args.MakeArgString(Triple));
     else if (Triple == DAL.getLastArgValue(OPT_triple_EQ))