cppfiles.c: Read files in, using mmap if possible, then prescan them separately.

	* cppfiles.c: Read files in, using mmap if possible, then
	prescan them separately.
	(read_file, read_with_read): New functions.
	* cpplex.c: Don't define UCHAR_MAX.
	(_cpp_read_and_prescan): Rename to _cpp_prescan.  Don't read
	the file here.

	* cppinit.c (handle_option): Automatically define __cplusplus,
	__OBJC__, __ASEEMBLER__, _LANGUAGE_FORTRAN here when we see
	the respective -lang switch.

	* cpphash.h (enum node_type, struct hashnode, _cpp_lookup
	prototype): Move to...
	* cpplib.h: ... here.  Rename struct hashnode to struct
	cpp_hashnode and give it a typedef.  Rename _cpp_lookup to
	cpp_lookup.  Add 'fe_value' slot, a union tree_node *.

From-SVN: r34228