openmp: Fix ICE on requires clause with atomic_default_mem_order (

openmp: Fix ICE on requires clause with atomic_default_mem_order (

When working on error directive, I've noticed the C FE ICEs on
  #pragma omp requires atomic_default_mem_order (
where it tries to peek 2nd token after the CPP_PRAGMA_EOL (or CPP_EOF)
in there in order to improve error-recovery on say
atomic_default_mem_order (acquire)
or
atomic_default_mem_order (seqcst)
etc.  The C++ FE didn't ICE, but it is better to follow the same thing there.

2021-08-19  Jakub Jelinek  <jakub@redhat.com>

gcc/c/
	* c-parser.c (c_parser_omp_requires): Don't call
	c_parser_peek_2nd_token and optionally consume token if current
	token is CPP_EOF, CPP_PRAGMA_EOL or CPP_CLOSE_PAREN.
gcc/cp/
	* parser.c (cp_parser_omp_requires): Don't call cp_lexer_nth_token_is
	and optionally consume token if current token is CPP_EOF,
	CPP_PRAGMA_EOL or CPP_CLOSE_PAREN.
gcc/testsuite/
	* c-c++-common/gomp/requires-3.c: Add testcase for
	atomic_default_mem_order ( at the end of line without corresponding ).