This patch (a combination of several previous patches by Cesar) adds
support for OpenACC 2.5's "declare create" directive with Fortran
allocatable variables (2.13.2. create clause). Allocate and deallocate
statements now allocate/deallocate memory on the target device as well
as on the host.

This works by triggering expansion of executable OpenACC
directives ("enter data" or "exit data") with new
GOMP_MAP_DECLARE_ALLOCATE or GOMP_MAP_DECLARE_DEALLOCATE clauses when
those statements are seen. Unlike other OpenACC functionality, no
additional explicit markup is required in the user's code.

This patch depends on the patch implementing GOMP_MAP_FIRSTPRIVATE_INT
for OpenACC, posted here:

https://gcc.gnu.org/ml/gcc-patches/2018-09/msg01202.html

Tested alongside that patch with offloading to NVPTX, and bootstrapped.
OK for trunk?

Thanks,

Julian

ChangeLog

2018-09-20  Cesar Philippidis  <cesar@codesourcery.com>
            Julian Brown  <julian@codesourcery.com>

	gcc/
	* omp-low.c (scan_sharing_clauses): Update handling of OpenACC declare
	create, declare copyin and declare deviceptr to have local lifetimes.
	(convert_to_firstprivate_int): Handle pointer types.
	(convert_from_firstprivate_int): Likewise.  Create local storage for
	the values being pointed to.  Add new orig_type argument.
	(lower_omp_target): Handle GOMP_MAP_DECLARE_{ALLOCATE,DEALLOCATE}.
	Add orig_type argument to convert_from_firstprivate_int call.
	Allow pointer types with GOMP_MAP_FIRSTPRIVATE_INT.  Don't privatize
	firstprivate VLAs.
	* tree-pretty-print.c (dump_omp_clause): Handle
	GOMP_MAP_DECLARE_{ALLOCATE,DEALLOCATE}.

	gcc/fortran/
	* gfortran.h (enum gfc_omp_map_op): Add OMP_MAP_DECLARE_ALLOCATE,
	OMP_MAP_DECLARE_DEALLOCATE.
	(gfc_omp_clauses): Add update_allocatable.
	* trans-array.c (trans-stmt.h): Include.
	(gfc_array_allocate): Call gfc_trans_oacc_declare_allocate for decls
	that have oacc_declare_create attribute set.
	* trans-decl.c (add_attributes_to_decl): Enable lowering of OpenACC
	declare create, declare copyin and declare deviceptr clauses.
	(add_clause): Don't duplicate OpenACC declare clauses.  Populate
	sym->backend_decl so that it can be used to determine if two symbols are
	unique.
	(find_module_oacc_declare_clauses): Relax oacc_declare_create to
	OMP_MAP_ALLOC, and oacc_declare_copyin to OMP_MAP_TO, in order to 
	match OpenACC 2.5 semantics.
	* trans-openmp.c (gfc_trans_omp_clauses): Use GOMP_MAP_ALWAYS_POINTER
	(for update directive) or GOMP_MAP_FIRSTPRIVATE_POINTER (otherwise) for
	allocatable scalar decls.  Handle OMP_MAP_DECLARE_{ALLOCATE,DEALLOCATE}
	clauses.
	(gfc_trans_oacc_executable_directive): Use GOMP_MAP_ALWAYS_POINTER
	for allocatable scalar data clauses inside acc update directives.
	(gfc_trans_oacc_declare_allocate): New function.
	* trans-stmt.c (gfc_trans_allocate): Call
	gfc_trans_oacc_declare_allocate for decls with oacc_declare_create
	attribute set.
	(gfc_trans_deallocate): Likewise.
	* trans-stmt.h (gfc_trans_oacc_declare_allocate): Declare.

	gcc/testsuite/
	* gfortran.dg/goacc/declare-allocatable-1.f90: New test.

	include/
	* gomp-constants.h (enum gomp_map_kind): Define
	GOMP_MAP_DECLARE_{ALLOCATE,DEALLOCATE} and GOMP_MAP_FLAG_SPECIAL_4.

	libgomp/
	* oacc-mem.c (gomp_acc_declare_allocate): New function.
	* oacc-parallel.c (GOACC_enter_exit_data): Handle
	GOMP_MAP_DECLARE_{ALLOCATE,DEALLOCATE}.
	* testsuite/libgomp.oacc-fortran/allocatable-array.f90: New test.
	* testsuite/libgomp.oacc-fortran/allocatable-scalar.f90: New test. 
	* testsuite/libgomp.oacc-fortran/declare-allocatable-1.f90: New test.
	* testsuite/libgomp.oacc-fortran/declare-allocatable-2.f90: New test.
	* testsuite/libgomp.oacc-fortran/declare-allocatable-3.f90: New test.
	* testsuite/libgomp.oacc-fortran/declare-allocatable-4.f90: New test.