[lld-macho] Add support for -w

This flag suppresses warnings produced by the linker. In ld64 this has
an interesting interaction with -fatal_warnings, it silences the
warnings but the link still fails. Instead of doing that here we still
print the warning and eagerly fail the link in case both are passed,
this seems more reasonable so users can understand why the link fails.

Differential Revision: https://reviews.llvm.org/D127564

lld/Common/ErrorHandler.cpp

@@ -242,6 +242,9 @@ void ErrorHandler::warn(const Twine &msg) {
     return;
   }
 
+  if (suppressWarnings)
+    return;
+
   std::lock_guard<std::mutex> lock(mu);
   reportDiagnostic(getLocation(msg), Colors::MAGENTA, "warning", msg);
   sep = getSeparator(msg);

lld/MachO/DriverUtils.cpp

@@ -87,6 +87,7 @@ InputArgList MachOOptTable::parse(ArrayRef<const char *> argv) {
   // Handle -fatal_warnings early since it converts missing argument warnings
   // to errors.
   errorHandler().fatalWarnings = args.hasArg(OPT_fatal_warnings);
+  errorHandler().suppressWarnings = args.hasArg(OPT_w);
 
   if (missingCount)
     error(Twine(args.getArgString(missingIndex)) + ": missing argument");

lld/MachO/Options.td

@@ -887,7 +887,6 @@ def e : Separate<["-"], "e">,
     Group<grp_rare>;
 def w : Flag<["-"], "w">,
     HelpText<"Suppress all warnings">,
-    Flags<[HelpHidden]>,
     Group<grp_rare>;
 def final_output : Separate<["-"], "final_output">,
     MetaVarName<"<name>">,

lld/include/lld/Common/ErrorHandler.h

@@ -101,6 +101,7 @@ class ErrorHandler {
   StringRef logName = "lld";
   bool exitEarly = true;
   bool fatalWarnings = false;
+  bool suppressWarnings = false;
   bool verbose = false;
   bool vsDiagnostics = false;
   bool disableOutput = false;

lld/test/MachO/fatal-warnings.s

@@ -6,6 +6,12 @@
 # RUN: not %no-fatal-warnings-lld %t1.o -fatal_warnings -o /dev/null \
 # RUN:     -single_module 2>&1 | FileCheck -check-prefix=ERROR %s
 
+# RUN: %no-fatal-warnings-lld %t1.o -w -o /dev/null -single_module 2>&1 \
+# RUN:     | count 0
+# RUN: not %no-fatal-warnings-lld %t1.o -fatal_warnings -w -o /dev/null \
+# RUN:     -single_module 2>&1 \
+# RUN:     | FileCheck --check-prefix=ERROR %s
+
 # ERROR: error: Option `-single_module' is deprecated
 # WARNING: warning: Option `-single_module' is deprecated