Support UTF-8 identifiers in C/C++ expressions (PR gdb/22973)

Support UTF-8 identifiers in C/C++ expressions (PR gdb/22973)

Factor out cp_ident_is_alpha/cp_ident_is_alnum out of
gdb/cp-name-parser.y and use it in the C/C++ expression parser too.

New test included.

gdb/ChangeLog:
2018-05-22  Pedro Alves  <palves@redhat.com>
	    張俊芝  <zjz@zjz.name>

	PR gdb/22973
	* c-exp.y: Include "c-support.h".
	(parse_number, c_parse_escape, lex_one_token): Use TOLOWER instead
	of tolower.  Use c_ident_is_alpha to scan names.
	* c-lang.c: Include "c-support.h".
	(convert_ucn, convert_octal, convert_hex, convert_escape): Use
	ISXDIGIT instead of isxdigit and ISDIGIT instead of isdigit.
	* c-support.h: New file, with bits factored out from ...
	* cp-name-parser.y: ... this file.
	Include "c-support.h".
	(cp_ident_is_alpha, cp_ident_is_alnum): Deleted, moved to
	c-support.h and renamed.
	(symbol_end, yylex): Adjust.

gdb/testsuite/ChangeLog:
2018-05-22  Pedro Alves  <palves@redhat.com>

	PR gdb/22973
	* gdb.base/utf8-identifiers.c: New file.
	* gdb.base/utf8-identifiers.exp: New file.