* cppcharset.c (one_utf8_to_cppchar, one_cppchar_to_utf8,
	one_utf8_to_utf32, one_utf32_to_utf8, one_utf8_to_utf16,
	one_utf16_to_utf8, conversion_loop, convert_utf8_utf16,
	convert_utf8_utf32, convert_utf16_utf8,	convert_utf32_utf8,
	convert_no_conversion, convert_using_iconv): New functions.
	(APPLY_CONVERSION): New macro.
	(struct conversion, conversion_tab): New data structure.
	(init_iconv_desc): Check conversion_tab for a custom conversion
	primitive before trying to use iconv.
	(convert_cset): Deleted.
	(cpp_init_iconv): Use UTF- terminology, not UCS-.
	(_cpp_destroy_iconv): Update to match.
	(_cpp_valid_ucn): We don't need iconv to implement UCNs.
	(convert_ucn): Use one_cppchar_to_utf8 and APPLY_CONVERSION.
	(convert_escape, cpp_interpret_string): Use APPLY_CONVERSION.
	(_cpp_interpret_string_notranslate): New function, moved here
	from cpplib.c.

	* cpphash.h (convert_f, struct cset_converter): New types.
	(struct cpp_reader): narrow_cset_desc and wide_cset_desc
	are now struct cset_converter, not bare iconv_t.
	Update prototypes.
	* cpplib.c (interpret_string_notranslate): Moved to cppcharset.c;
	all callers changed.

From-SVN: r69204