[clang][driver] Rename DriverOption as NoXarchOption (NFC)

As discussed in [1], ClangFlags::DriverOption is currently only used to
mark options that should not be forwarded to other tools via `-Xarch`
options. This patch renames this flag accordingly and updates the
corresponding driver diagnostic.

A comment in ToolChain::TranslateXarchArgs is also updated to reflect
the change. The original comment referred to isDriverOption(), which is
no longer available.

[1] http://lists.llvm.org/pipermail/cfe-dev/2020-October/066953.html

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D89799

Author: banach-space

clang/include/clang/Basic/DiagnosticDriverKinds.td

@@ -121,8 +121,6 @@ def err_drv_missing_argument : Error<
   "argument to '%0' is missing (expected %1 value%s1)">;
 def err_drv_invalid_Xarch_argument_with_args : Error<
   "invalid Xarch argument: '%0', options requiring arguments are unsupported">;
-def err_drv_invalid_Xarch_argument_isdriver : Error<
-  "invalid Xarch argument: '%0', cannot change driver behavior inside Xarch argument">;
 def err_drv_Xopenmp_target_missing_triple : Error<
   "cannot deduce implicit triple value for -Xopenmp-target, specify triple using -Xopenmp-target=<triple>">;
 def err_drv_invalid_Xopenmp_target_with_args : Error<

clang/include/clang/Driver/Driver.h

@@ -314,7 +314,7 @@ class Driver {
 
   const llvm::opt::OptTable &getOpts() const { return getDriverOptTable(); }
 
-  const DiagnosticsEngine &getDiags() const { return Diags; }
+  DiagnosticsEngine &getDiags() const { return Diags; }
 
   llvm::vfs::FileSystem &getVFS() const { return *VFS; }
 

clang/include/clang/Driver/Options.h

@@ -24,7 +24,7 @@ namespace options {
 /// Flags specifically for clang options.  Must not overlap with
 /// llvm::opt::DriverFlag.
 enum ClangFlags {
-  DriverOption = (1 << 4),
+  NoXarchOption = (1 << 4),
   LinkerInput = (1 << 5),
   NoArgumentUnused = (1 << 6),
   Unsupported = (1 << 7),