[clang] Remove CLANG_ROUND_TRIP_CC1_ARGS and always roundtrip in +assert builds

[thakis]

Summary

This removes the ability to disable roundtripping in assert builds.
(Roundtripping happens by default in assert builds both before and after
this patch.)

The CLANG_ROUND_TRIP_CC1_ARGS was added as an escape hatch 9 months ago
in https://reviews.llvm.org/D97462, with a FIXME to remove it eventually.
It's probably time to remove it.

[dexonsmith]

SGTM; I'll let @jansvoboda11 confirm though.

[jansvoboda11]

LGTM, thanks!

[jansvoboda11]

clang/lib/Frontend/CompilerInvocation.cpp

614–615

Can you also update this comment that menions CLANG_ROUND_TRIP_CC1_ARGS?

[thakis]

clang/lib/Frontend/CompilerInvocation.cpp

614–615

Done, thanks!

clang/CMakeLists.txt

option(CLANG_BUILD_TOOLS
   "Build the Clang tools. If OFF, just generate build targets." ON)
 
 option(CLANG_ENABLE_ARCMT "Build ARCMT." ON)
 option(CLANG_ENABLE_STATIC_ANALYZER
   "Include static analyzer in clang binary." ON)
 
 option(CLANG_ENABLE_PROTO_FUZZER "Build Clang protobuf fuzzer." OFF)
 
-option(CLANG_ROUND_TRIP_CC1_ARGS
-  "Round-trip command line arguments in -cc1." ${LLVM_ENABLE_ASSERTIONS})
-
 if(NOT CLANG_ENABLE_STATIC_ANALYZER AND CLANG_ENABLE_ARCMT)
   message(FATAL_ERROR "Cannot disable static analyzer while enabling ARCMT or Z3")
 endif()
 
 if(CLANG_ENABLE_ARCMT)
   set(CLANG_ENABLE_OBJC_REWRITER ON)
 endif()
 
-if (CLANG_ROUND_TRIP_CC1_ARGS)
-  add_definitions(-DCLANG_ROUND_TRIP_CC1_ARGS=ON)
-endif()
-
 # Clang version information
 set(CLANG_EXECUTABLE_VERSION
     "${CLANG_VERSION_MAJOR}" CACHE STRING
     "Major version number that will be appended to the clang executable name")
 set(LIBCLANG_LIBRARY_VERSION
     "${CLANG_VERSION_MAJOR}" CACHE STRING
     "Major version number that will be appended to the libclang library")
 mark_as_advanced(CLANG_EXECUTABLE_VERSION LIBCLANG_LIBRARY_VERSION)

clang/lib/Frontend/CompilerInvocation.cpp

using ParseFn =
     llvm::function_ref<bool(CompilerInvocation &, ArrayRef<const char *>,
                             DiagnosticsEngine &, const char *)>;
 
 // Generate command line arguments from CompilerInvocation.
 using GenerateFn = llvm::function_ref<void(
     CompilerInvocation &, SmallVectorImpl<const char *> &,
     CompilerInvocation::StringAllocator)>;
 
 // May perform round-trip of command line arguments. By default, the round-trip
-// is enabled if CLANG_ROUND_TRIP_CC1_ARGS was defined during build. This can be
-// overwritten at run-time via the "-round-trip-args" and "-no-round-trip-args"
-// command line flags.
+// is enabled in assert builds. This can be overwritten at run-time via the
+// "-round-trip-args" and "-no-round-trip-args" command line flags.
 // During round-trip, the command line arguments are parsed into a dummy
 // instance of CompilerInvocation which is used to generate the command line
 // arguments again. The real CompilerInvocation instance is then created by
 // parsing the generated arguments, not the original ones.
 static bool RoundTrip(ParseFn Parse, GenerateFn Generate,
                       CompilerInvocation &RealInvocation,
                       CompilerInvocation &DummyInvocation,
                       ArrayRef<const char *> CommandLineArgs,
                       DiagnosticsEngine &Diags, const char *Argv0) {
-  // FIXME: Switch to '#ifndef NDEBUG' when possible.
-#ifdef CLANG_ROUND_TRIP_CC1_ARGS
+#ifndef NDEBUG
   bool DoRoundTripDefault = true;
 #else
   bool DoRoundTripDefault = false;
 #endif
 
   bool DoRoundTrip = DoRoundTripDefault;
   for (const auto *Arg : CommandLineArgs) {
     if (Arg == StringRef("-round-trip-args"))