Revert back to only ignoring -wmo

Ignoring both `-wmo` and `-index-file` will be harder than just `-wmo`. This is because when calling the compiler and passing `-index-file` after `-dump-ast`, the option gets un-ignored by `Driver::buildOutputInfo`. Therefore, we will just ignore `-wmo` for now.

Author: vinivendra

include/swift/AST/DiagnosticsDriver.def

@@ -166,8 +166,8 @@ WARNING(warn_opt_remark_disabled, none,
 WARNING(warn_ignoring_batch_mode,none,
 "ignoring '-enable-batch-mode' because '%0' was also specified", (StringRef))
 
-WARNING(warn_ignoring_single_compile, none,
-        "ignoring '%0' because '-dump-ast' was also specified", (StringRef))
+WARNING(warn_ignoring_wmo, none,
+        "ignoring '-wmo' because '-dump-ast' was also specified", ())
 
 WARNING(warn_ignoring_source_range_dependencies,none,
 "ignoring '-enable-source-range-dependencies' because '%0' was also specified", (StringRef))

lib/Driver/Driver.cpp

@@ -1758,13 +1758,14 @@ Driver::computeCompilerMode(const DerivedArgList &Args,
   const Arg *ArgRequiringSinglePrimaryCompile =
       Args.getLastArg(options::OPT_enable_source_range_dependencies);
 
-  // AST dump doesn't work with `-wmo` or `-index-file`. Since it's not common
-  // to want to dump the AST, we assume that's the priority and ignore the
-  // conflicting option, but we warn the user about this decision.
-  if (ArgRequiringSingleCompile &&
+  // AST dump doesn't work with `-wmo`. Since it's not common to want to dump
+  // the AST, we assume that's the priority and ignore `-wmo`, but we warn the
+  // user about this decision.
+  // FIXME: AST dump also doesn't work with `-index-file`, but that fix is a bit
+  // more complicated than this.
+  if (Args.hasArg(options::OPT_whole_module_optimization) &&
       Args.hasArg(options::OPT_dump_ast)) {
-    Diags.diagnose(SourceLoc(), diag::warn_ignoring_single_compile,
-                   ArgRequiringSingleCompile->getOption().getPrefixedName());
+    Diags.diagnose(SourceLoc(), diag::warn_ignoring_wmo);
     return OutputInfo::Mode::StandardCompile;
   }