cppfiles.c: Move all default-#defines to top of file.

cppfiles.c: Move all default-#defines to top of file.

	* cppfiles.c: Move all default-#defines to top of file.
	(open_include_file): Replace by lookup_include_file.
	(read_with_read, read_file): Merged into read_include_file.
	(stack_include_file, purge_cache): New functions.
	(close_cached_fd): Delete.
	(lookup_include_file, read_include_file, _cpp_pop_file_buffer):
	Cache the in-memory buffer, not the file descriptor.

	* cpphash.h (struct include_file): Add buffer, st, refcnt,
	mapped fields.
	(xcnew): New utility macro.
	(DO_NOT_REREAD, NEVER_REREAD): Move up by struct include_file.
	* cpplib.h (struct cpp_buffer): Remove mapped field.

	* cpplex.c (parse_string): Accept backslash space newline as a
	line continuation.
	(lex_line): Likewise.
	(_cpp_get_token): Remove hard limit on macro nesting.

testsuite:
	* gcc.dg/cpp/backslash.c: New test.

From-SVN: r36347