[clang][FMV] Pass the '+fmv' target-feature when FMV is enabled.

This will allow the backend to enable the corresponding subtarget
feature (FeatureFMV), which in turn can be queried for llvm codegen
decisions. See llvm#87939 for example.

clang/lib/Driver/ToolChains/Clang.cpp

@@ -7815,13 +7815,14 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
 
   addOutlineAtomicsArgs(D, getToolChain(), Args, CmdArgs, Triple);
 
-  if (Triple.isAArch64() &&
-      (Args.hasArg(options::OPT_mno_fmv) ||
-       (Triple.isAndroid() && Triple.isAndroidVersionLT(23)) ||
-       getToolChain().GetRuntimeLibType(Args) != ToolChain::RLT_CompilerRT)) {
-    // Disable Function Multiversioning on AArch64 target.
+  if (Triple.isAArch64()) {
     CmdArgs.push_back("-target-feature");
-    CmdArgs.push_back("-fmv");
+    if (Args.hasArg(options::OPT_mno_fmv) ||
+        (Triple.isAndroid() && Triple.isAndroidVersionLT(23)) ||
+        getToolChain().GetRuntimeLibType(Args) != ToolChain::RLT_CompilerRT)
+      CmdArgs.push_back("-fmv");
+    else
+      CmdArgs.push_back("+fmv");
   }
 
   if (Args.hasFlag(options::OPT_faddrsig, options::OPT_fno_addrsig,

clang/test/Driver/aarch64-features.c

@@ -24,6 +24,7 @@
 
 // CHECK-FMV-OFF: "-target-feature" "-fmv"
 // CHECK-FMV-NOT: "-target-feature" "-fmv"
+// CHECK-FMV:     "-target-feature" "+fmv"
 
 // Check for AArch64 out-of-line atomics default settings.
 // RUN: %clang --target=aarch64-linux-android -rtlib=compiler-rt \