regex: rename remaining __attribute calls to __attribute__.

regex: rename remaining __attribute calls to __attribute__.

Commit 930b85b changed definition of __attribute, but left some uses
unchanged, preventing compilation of regex module on most non-gcc
environments:
* lib/regcomp.c (re_set_fastmap, seek_collating_symbol_entry)
(lookup_collation_sequence_value, build_range_exp)
(build_collating_symbol): Set attributes with newly renamed
__attribute__ decorator.
* lib/regex_internal.c (re_string_peek_byte_case)
(re_node_set_compare, re_node_set_contains): Likewise.
* lib/regexec.c (acquire_init_state_context): Likewise.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>