Have llvm-mc --version print the list of registered targets like llc does.

Patch by jey.

llvm-svn: 152315

llvm/tools/llvm-mc/llvm-mc.cpp

@@ -512,6 +512,9 @@ int main(int argc, char **argv) {
   llvm::InitializeAllAsmParsers();
   llvm::InitializeAllDisassemblers();
 
+  // Register the target printer for --version.
+  cl::AddExtraVersionPrinter(TargetRegistry::printRegisteredTargetsForVersion);
+
   cl::ParseCommandLineOptions(argc, argv, "llvm machine code playground\n");
   TripleName = Triple::normalize(TripleName);
   setDwarfDebugFlags(argc, argv);