libcpp: registering both a pragma and a pragma namespace with the same name

[Aldy Hernandez <aldyh at redhat dot com>]

Hi Tom.  Hi folks.

We've asked Balaji to rewrite the <#pragma simd> handling for cilkplus 
as we currently do for OMP, etc, in init_pragma().

The cilkplus branch currently has something like:

      cpp_register_deferred_pragma (parse_in, "simd", "",
                                  PRAGMA_SIMD_EMPTY, true, false);
      cpp_register_deferred_pragma (parse_in, "simd", "assert",
	                            PRAGMA_SIMD_ASSERT, true, false);
      cpp_register_deferred_pragma (parse_in, "simd", "noassert",
	                            PRAGMA_SIMD_NOASSERT, true, false);
      cpp_register_deferred_pragma (parse_in, "simd", "vectorlength",
	                            PRAGMA_SIMD_VECTORLENGTH, true, false);

Notice that #pragma simd can be both a pragma name space, and also a 
lone pragma with no arguments:

	#pragma simd assert
		-or-
	#pragma simd

It seems like the code in libcpp's do_pragma(), specifically disallows 
this.  If we're looking at a possible pragma name space, the next 
expected token is a CPP_NAME.

Is there a way to handle this scenario with the current infrastructure? 
 If not, is something like the attached (untested) patch reasonable?

Aldy

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