[lld-macho] Ignore -debug_variant flag

[keith]

Summary

As far as I can tell all this flag does in ld64 is warn about cases
where you're building dylibs that are going to be part of the shared
cache, which I assume only apple is doing. Strangely I have seen this
flag being passed in the wild so this silences the warning about it.

lld/MachO/Options.td

 def no_inits : Flag<["-"], "no_inits">,
     HelpText<"Fail if the output contains static initializers">,
     Flags<[HelpHidden]>,
     Group<grp_rare>;
 def no_warn_inits : Flag<["-"], "no_warn_inits">,
     HelpText<"Suppress warnings for static initializers in the output">,
     Flags<[HelpHidden]>,
     Group<grp_rare>;
-def debug_variant : Flag<["-"], "debug_variant">,
-    HelpText<"Suppress warnings germane to binaries shipping to customers">,
-    Flags<[HelpHidden]>,
-    Group<grp_rare>;
 def unaligned_pointers : Separate<["-"], "unaligned_pointers">,
     MetaVarName<"<treatment>">,
     HelpText<"Handle unaligned pointers in __DATA segments according to <treatment>: warning, error, or suppress (default for arm64e is error, otherwise suppress)">,
     Flags<[HelpHidden]>,
     Group<grp_rare>;
 def dirty_data_list : Separate<["-"], "dirty_data_list">,
     MetaVarName<"<path>">,
     HelpText<"Specify data symbols in <path> destined for the __DATA_DIRTY segment">,
def new_linker : Flag<["-"], "new_linker">,
     Group<grp_ignored>;
 
 def grp_ignored_silently : OptionGroup<"ignored_silently">, HelpText<"IGNORED SILENTLY">;
 
 def objc_abi_version : Separate<["-"], "objc_abi_version">,
     HelpText<"This option only applies to i386 in ld64">,
     Flags<[HelpHidden]>,
     Group<grp_ignored_silently>;
+def debug_variant : Flag<["-"], "debug_variant">,
+    HelpText<"Do not warn about issues that are only problems for binaries shipping to customers.">,
+    Flags<[HelpHidden]>,
+    Group<grp_ignored_silently>;

lld/test/MachO/silent-ignore.s

 # RUN:   -objc_abi_version 2 \
 # RUN:   -ios_simulator_version_min 9.0.0 \
 # RUN:   -sdk_version 13.2
 # RUN: not %lld -v --not-an-ignored-argument 2>&1 | FileCheck %s
 # CHECK: error: unknown argument '--not-an-ignored-argument'
 
 ## Check that we don't emit any warnings nor errors for these unimplemented flags.
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t.o
-# RUN: %lld %t.o -o /dev/null -objc_abi_version 2
+# RUN: %lld %t.o -o /dev/null -objc_abi_version 2 -debug_variant
 
 .globl _main
 _main:
   ret