OpenMP: Parse align clause in allocate directive in C/C++

gcc/c/ChangeLog:

	* c-parser.cc (c_parser_omp_allocate): Parse align
	clause and check for restrictions.

gcc/cp/ChangeLog:

	* parser.cc (cp_parser_omp_allocate): Parse align
	clause and check for restrictions.

gcc/testsuite/ChangeLog:

	* c-c++-common/gomp/allocate-5.c: Extend for align clause.