Fix some incompatibilities with gcc -ansi -pedantic.

Fix some incompatibilities with gcc -ansi -pedantic.
* lib/regex.h (__restrict_arr): Don't use the [restrict] syntax
if compiling pedantically with GCC, unless it's C99 or later.
Don't trust sys/cdefs.h's definition of __restrict_arr, either, as
it mishandles gcc -ansi -pedantic as well.
* lib/regex_internal.h (re_token_t): Don't use enum bitfields
if gcc -pedantic.
* lib/regexec.c (check_node_accept_bytes): Don't use auto
initializers for struct if -pedantic, unless it's C99 or later.