[Driver] Unsupport --print-multiarch

* 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 #51469

Reviewed By: phosek

Differential Revision: https://reviews.llvm.org/D133170

clang/include/clang/Driver/Options.td

@@ -4069,8 +4069,9 @@ 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">,

clang/lib/Driver/Driver.cpp

@@ -2152,12 +2152,6 @@ bool Driver::HandleImmediateArgs(const Compilation &C) {
     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;

clang/test/Driver/print-multiarch.c

@@ -1,6 +1,6 @@
-// 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'