OpenMP: uses_allocators with ';'-separated list

OpenMP: uses_allocators with ';'-separated list

OpenMP 6.0 has the following wording for the uses_allocators clause:
"More than one clause-argument-specification may be specified";
this permits ';' lists. While that's pointless for predefined
allocators, for user-defined allocators it saves redundant
') uses_allocators(' by permitting:
  uses_allocators( traits(t1): alloc1 ; traits(t2): alloc2 )

Additionally, the order in the tree dump has been changed to
place the modifiers before the allocator variable, matching
the input syntax.

gcc/c/ChangeLog:

	* c-parser.cc (c_parser_omp_clause_uses_allocators): Accept
	multiple clause-argument-specifications separated by ';'.

gcc/cp/ChangeLog:

	* parser.cc (cp_parser_omp_clause_uses_allocators): Accept
	multiple clause-argument-specifications separated by ';'.

gcc/fortran/ChangeLog:

	* openmp.cc (gfc_match_omp_clause_uses_allocators): Accept
	multiple clause-argument-specifications separated by ';'.

gcc/ChangeLog:

	* tree-pretty-print.cc (dump_omp_clause): For uses_allocators,
	print modifier before allocator variable.

libgomp/ChangeLog:

	* testsuite/libgomp.fortran/uses_allocators-7.f90: Add ';' test.

gcc/testsuite/ChangeLog:

	* c-c++-common/gomp/uses_allocators-8.c: New test.