[llvm] [clang] [SPARC] Consume `tune-cpu` directive in the backend (PR #77195)

[via cfe-commits]

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@@ -5119,7 +5119,7 @@ def module_file_info : Flag<["-"], "module-file-info">, Flags<[]>,
   HelpText<"Provide information about a particular module file">;
 def mthumb : Flag<["-"], "mthumb">, Group<m_Group>;
 def mtune_EQ : Joined<["-"], "mtune=">, Group<m_Group>,
-  HelpText<"Only supported on AArch64, PowerPC, RISC-V, SystemZ, and X86">;
+  HelpText<"Only supported on AArch64, PowerPC, RISC-V, SPARC, SystemZ, and X86">;
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koachan wrote:

Yep, the part responsible in clang already exists [here](https://github.com/llvm/llvm-project/blob/ac8b4f874945f83eec8c8f56d9fc80093e02a7b2/clang/lib/Driver/ToolChains/Clang.cpp#L2135-L2145) and there's already some test case too:
https://github.com/llvm/llvm-project/blob/main/clang/test/Driver/sparc-mtune.c

Should I add more tests?

https://github.com/llvm/llvm-project/pull/77195