* cppfiles.c (stack_include_file): Check for stacked contexts

	* cppfiles.c (stack_include_file): Check for stacked contexts
	here.
	* cpphash.h (_cpp_do__Pragma): New prototype.
	* cppinit.c (cpp_reader_init): Add _Pragma keyword to hash table.

	* cpplex.c (skip_escaped_newlines): Only process trigraphs and
	escaped newlines if !(buffer->from_stage3).
	(_cpp_lex_token): Warn about missing newlines iff
	!buffer->from_stage3.

	* cpplib.c (get__Pragma_string, destringize,
	_cpp_do__Pragma): New functions.
	(run_directive): Set output_line for _Pragma to avoid line
	markers in output.  Set from_stage3 and prevent macro expansion
	for _Pragma and command-line options.  Check buffer exhaustion.
	(cpp_push_buffer): Don't check for stacked macro contexts, as
	this is perfectly legitimate for _Pragma.  Move the check to
	stack_include_file instead. Set from_stage3 iff buffer is
	preprocessed input.

	* cpplib.h (struct cpp_buffer): Make warned_cplusplus_comments
	unsigned. New boolean from_stage3.
	(struct spec_nodes): Add n__Pragma.

	* cppmacro.c (enter_macro_context): Flip sense of return value.
	(_cpp_get_token): Handle _Pragma operator.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@37147 138bc75d-0d04-0410-961f-82ee72b054a4