[Driver] Unsupport --print-multiarch

[MaskRay]

Summary

• If GCC is configured with --disable-multi-arch, --print-multiarch output is an empty line.
• If GCC is configured with --enable-multi-arch, --print-multiarch output may be a normalized triple or (on Debian, 'vendor' is omitted) x86_64-linux-gnu.

The Clang support D101400 just prints the Debian multiarch style triple
unconditionally, but the string is not really expected for non-Debian systems.

AIUI many Linux distributions and non-Linux OSes don't configure GCC with --enable-multi-arch.
Instead of getting us in the trouble of supporting all kinds of variants, drop the support as before D101400.

Close https://github.com/llvm/llvm-project/issues/51469

[phosek]

LGTM

clang/include/clang/Driver/Options.td

 def print_multi_directory : Flag<["-", "--"], "print-multi-directory">;
 def print_multi_lib : Flag<["-", "--"], "print-multi-lib">;
 def print_multi_os_directory : Flag<["-", "--"], "print-multi-os-directory">,
   Flags<[Unsupported]>;
 def print_target_triple : Flag<["-", "--"], "print-target-triple">,
   HelpText<"Print the normalized target triple">, Flags<[FlangOption]>;
 def print_effective_triple : Flag<["-", "--"], "print-effective-triple">,
   HelpText<"Print the effective target triple">, Flags<[FlangOption]>;
-def print_multiarch : Flag<["-", "--"], "print-multiarch">,
-  HelpText<"Print the multiarch target triple">;
+// GCC --disable-multiarch, GCC --enable-multiarch (upstream and Debian
+// specific) have different behaviors. We choose not to support the option.
+def : Flag<["-", "--"], "print-multiarch">, Flags<[Unsupported]>;
 def print_prog_name_EQ : Joined<["-", "--"], "print-prog-name=">,
   HelpText<"Print the full program path of <name>">, MetaVarName<"<name>">;
 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">;

clang/lib/Driver/Driver.cpp

bool Driver::HandleImmediateArgs(const Compilation &C) {
   }
 
   if (C.getArgs().hasArg(options::OPT_print_effective_triple)) {
     const llvm::Triple Triple(TC.ComputeEffectiveClangTriple(C.getArgs()));
     llvm::outs() << Triple.getTriple() << "\n";
     return false;
   }
 
-  if (C.getArgs().hasArg(options::OPT_print_multiarch)) {
-    llvm::outs() << TC.getMultiarchTriple(*this, TC.getTriple(), SysRoot)
-                 << "\n";
-    return false;
-  }
-
   if (C.getArgs().hasArg(options::OPT_print_targets)) {
     llvm::TargetRegistry::printRegisteredTargetsForVersion(llvm::outs());
     return false;
   }
 
   return true;
 }
 

clang/test/Driver/print-multiarch.c

-// Check the output of -print-multiarch.
+/// GCC --disable-multiarch, GCC --enable-multiarch (upstream and Debian specific) have different behaviors.
+/// We choose not to support the option.
 
-// RUN: %clang -print-multiarch --target=x86_64-unknown-linux-gnu \
-// RUN:        -resource-dir=%S/Inputs/resource_dir \
-// RUN:      | FileCheck --check-prefix=PRINT-MULTIARCH %s
-// PRINT-MULTIARCH: {{^}}x86_64-linux-gnu{{$}}
+// RUN: not %clang -print-multiarch --target=x86_64-unknown-linux-gnu 2>&1 | FileCheck %s
+
+// CHECK: error: unsupported option '-print-multiarch'