[clang] [llvm] [HIP][MacOS] Mach-O support and Darwin toolchain fixes (PR #183991)

[Paulius Velesko via llvm-commits]

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@@ -668,6 +668,16 @@ class ObjectFileHandler final : public FileHandler {
     StringSaver SS{Alloc};
     SmallVector<StringRef, 8u> ObjcopyArgs{"llvm-objcopy"};
 
+    // Detect if host object is Mach-O to skip unsupported flags.
+    bool IsObjectMachO = false;
+    {
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pvelesko wrote:

Didn't mean to push that. I was testing for enabling rdc for macos but after this we run into a problem of `__CLANG_OFFLOAD_BUNDLE__hip-spirv64-unknown-unknown-unknown-generic.`exceeding Mach-O  limit of 16 characters. So enabling rdc will require more work and can be done in a subsequent PR. 

https://github.com/llvm/llvm-project/pull/183991