Add -print-targets to print the registered targets

Differential Revision: https://reviews.llvm.org/D79565

clang/docs/ReleaseNotes.rst

@@ -130,6 +130,7 @@ Modified Compiler Flags
 - ``-fno-char8_t`` now disables the ``char8_t`` keyword, not just the use of
   ``char8_t`` as the character type of ``u8`` literals. This restores the
   Clang 8 behavior that regressed in Clang 9 and 10.
+- -print-targets has been added to print the registered targets.
 
 New Pragmas in Clang
 --------------------

clang/include/clang/Driver/Options.td

@@ -2804,6 +2804,8 @@ def print_resource_dir : Flag<["-", "--"], "print-resource-dir">,
   HelpText<"Print the resource directory pathname">;
 def print_search_dirs : Flag<["-", "--"], "print-search-dirs">,
   HelpText<"Print the paths used for finding libraries and programs">;
+def print_targets : Flag<["-", "--"], "print-targets">,
+  HelpText<"Print the registered targets">;
 def private__bundle : Flag<["-"], "private_bundle">;
 def pthreads : Flag<["-"], "pthreads">;
 def pthread : Flag<["-"], "pthread">, Flags<[CC1Option]>,

clang/lib/Driver/Driver.cpp

@@ -1815,6 +1815,11 @@ bool Driver::HandleImmediateArgs(const Compilation &C) {
     return false;
   }
 
+  if (C.getArgs().hasArg(options::OPT_print_targets)) {
+    llvm::TargetRegistry::printRegisteredTargetsForVersion(llvm::outs());
+    return false;
+  }
+
   return true;
 }