[clang] [clang][Driver][RISCV] Honor -m[no-]global-merge for RISC-V (PR #79372)

[Fangrui Song via cfe-commits]

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@@ -2129,6 +2129,16 @@ void Clang::AddRISCVTargetArgs(const ArgList &Args,
           << A->getSpelling() << Val;
     }
   }
+
+  // Forward the -mglobal-merge option for explicit control over the pass.
+  if (Arg *A = Args.getLastArg(options::OPT_mglobal_merge,
+                               options::OPT_mno_global_merge)) {
+    CmdArgs.push_back("-mllvm");
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MaskRay wrote:

I know that you are copying arm/aarch64, but for new code for a boolean option (sometimes called flag), we use a convention to only pass a non-default option to cc1.

Since `-riscv-enable-global-merge` defaults to 0, we only pass `-mllvm -riscv-enable-global-merge` to cc1 (remove `=true`).

https://github.com/llvm/llvm-project/pull/79372