Cleanup setup of gl_state in various parts of the code.

Cleanup setup of gl_state in various parts of the code.
* syntax.h (SETUP_BUFFER_SYNTAX_TABLE): New macro.
(SETUP_SYNTAX_TABLE, SETUP_SYNTAX_TABLE_FOR_OBJECT):
* syntax.c (find_defun_start, Fchar_syntax, Fmatching_paren, skip_chars):
* regex.c (regex_compile): Use it.
(re_compile_pattern): Don't set gl_state.current_syntax_table since
it's now set in regex_compile when/if we need it.