openmp: Add support for firstprivate and allocate clauses on scope construct

OpenMP 5.2 adds support for firstprivate and allocate clauses on the scope
construct and this patch adds that support to GCC.
5.2 unfortunately (IMNSHO mistakenly) marked scope construct as worksharing,
which implies that it isn't possible to nest inside of it other scope,
worksharing loop, sections, explicit barriers, single etc. which would
make scope far less useful.  I'm not implementing that part, keeping the
5.1 behavior here, and will file an issue to revert that for OpenMP 6.0.
But, for firstprivate it keeps the restriction that is now implied from
worksharing construct that listed var can't be private in outer context,
where for reduction 5.1 had similar restriction explicit even for scope
and 5.2 has it implicitly through worksharing construct.

2022-05-31  Jakub Jelinek  <jakub@redhat.com>

gcc/
	* omp-low.cc (build_outer_var_ref): For code == OMP_CLAUSE_ALLOCATE
	allow var to be private in the outer context.
	(lower_private_allocate): Pass OMP_CLAUSE_ALLOCATE as last argument
	to build_outer_var_ref.
gcc/c/
	* c-parser.cc (OMP_SCOPE_CLAUSE_MASK): Add firstprivate and allocate
	clauses.
gcc/cp/
	* parser.cc (OMP_SCOPE_CLAUSE_MASK): Add firstprivate and allocate
	clauses.
gcc/testsuite/
	* c-c++-common/gomp/scope-5.c: New test.
	* c-c++-common/gomp/scope-6.c: New test.
	* g++.dg/gomp/attrs-1.C (bar): Add firstprivate and allocate clauses
	to scope construct.
	* g++.dg/gomp/attrs-2.C (bar): Likewise.
libgomp/
	* testsuite/libgomp.c-c++-common/allocate-1.c (foo): Add testcase for
	scope construct with allocate clause.
	* testsuite/libgomp.c-c++-common/allocate-3.c (foo): Likewise.
	* testsuite/libgomp.c-c++-common/scope-2.c: New test.