[clang] [Clang][Driver] Fix target parsing for -fveclib=libmvec option. (PR #138288)

[Benjamin Maxwell via cfe-commits]

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@@ -934,7 +934,7 @@ void tools::addLTOOptions(const ToolChain &ToolChain, const ArgList &Args,
     std::optional<StringRef> OptVal =
         llvm::StringSwitch<std::optional<StringRef>>(ArgVecLib->getValue())
             .Case("Accelerate", "Accelerate")
-            .Case("LIBMVEC", "LIBMVEC-X86")
+            .Case("libmvec", "LIBMVEC-X86")
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MacDue wrote:

Oh right I see now :+1:  I assumed this StringSwitch was correct, but it looks like `-fveclib=libmvec` didn't work with LTO before (only LIBMVEC uppercase). 

https://github.com/llvm/llvm-project/pull/138288