[NFCI][SYCL] Correct -fdeclare-spirv-builtins to use marshalling (#3515)

The -fdeclare-spirv-builtins flag never got updated to use the
marshalling, so it causes a problem with the round-tripping.  However,
the solution we used (to call 'generate-arg' for it) is unnecessary with
the marshalling.

Author: Erich Keane

clang/include/clang/Driver/Options.td

@@ -5559,8 +5559,10 @@ def finclude_default_header : Flag<["-"], "finclude-default-header">,
   HelpText<"Include default header file for OpenCL">;
 def fdeclare_opencl_builtins : Flag<["-"], "fdeclare-opencl-builtins">,
   HelpText<"Add OpenCL builtin function declarations (experimental)">;
-def fdeclare_spirv_builtins : Flag<["-"], "fdeclare-spirv-builtins">,
-  HelpText<"Add SPIR-V builtin function declarations (experimental)">;
+def fdeclare_spirv_builtins
+    : Flag<["-"], "fdeclare-spirv-builtins">,
+      HelpText<"Add SPIR-V builtin function declarations (experimental)">,
+      MarshallingInfoFlag<LangOpts<"DeclareSPIRVBuiltins">>;
 
 def fpreserve_vec3_type : Flag<["-"], "fpreserve-vec3-type">,
   HelpText<"Preserve 3-component vector type">,

clang/lib/Frontend/CompilerInvocation.cpp

@@ -3502,8 +3502,6 @@ void CompilerInvocation::GenerateLangArgs(const LangOptions &Opts,
       LangOptions::SignReturnAddressKeyKind::BKey)
     GenerateArg(Args, OPT_msign_return_address_key_EQ, "b_key", SA);
 
-  if (Opts.DeclareSPIRVBuiltins)
-    GenerateArg(Args, OPT_fdeclare_spirv_builtins, SA);
 }
 
 bool CompilerInvocation::ParseLangArgs(LangOptions &Opts, ArgList &Args,
@@ -3594,8 +3592,6 @@ bool CompilerInvocation::ParseLangArgs(LangOptions &Opts, ArgList &Args,
     }
   }
 
-  Opts.DeclareSPIRVBuiltins = Args.hasArg(OPT_fdeclare_spirv_builtins);
-
   // These need to be parsed now. They are used to set OpenCL defaults.
   Opts.IncludeDefaultHeader = Args.hasArg(OPT_finclude_default_header);
   Opts.DeclareOpenCLBuiltins = Args.hasArg(OPT_fdeclare_opencl_builtins);