<built-in> vs <internal>

[Per Bothner]

While initializing, some code (including cpplib) sets the
current filename to "<built-in>" while other code (including
c_init_decl_processing) uses "<internal>".  What is the
distinction?  Any reason not to use "<built-in>" consistently?
Doing so would probably make the source_location/location_t
merge easier.  (A patch assuming this change is soming soon!)
-- 
	--Per Bothner
per@bothner.com   http://per.bothner.com/