Fix OpenMP's target update directive in templated code.

Fix OpenMP's target update directive in templated code.

    FAIL: g++.dg/gomp/tpl-target-update.C  -std=c++98 (internal compiler error)
    FAIL: g++.dg/gomp/tpl-target-update.C  -std=c++98 (test for excess errors)
    FAIL: g++.dg/gomp/tpl-target-update.C  -std=c++11 (internal compiler error)
    FAIL: g++.dg/gomp/tpl-target-update.C  -std=c++11 (test for excess errors)
    FAIL: g++.dg/gomp/tpl-target-update.C  -std=c++14 (internal compiler error)
    FAIL: g++.dg/gomp/tpl-target-update.C  -std=c++14 (test for excess errors)

    [...]/source-gcc/gcc/testsuite/g++.dg/gomp/tpl-target-update.C: In instantiation of 'void f(T, T) [with T = int]':
    [...]/source-gcc/gcc/testsuite/g++.dg/gomp/tpl-target-update.C:19:9:   required from here
    [...]/source-gcc/gcc/testsuite/g++.dg/gomp/tpl-target-update.C:10:9: internal compiler error: tree check: expected oacc_parallel or oacc_kernels or oacc_data or oacc_host_data or omp_parallel or omp_task or omp_for or omp_simd or cilk_simd or cilk_for or omp_distribute or oacc_loop or omp_teams or omp_target_data or omp_target or omp_sections or omp_single, have omp_target_update in tsubst_expr, at cp/pt.c:14209
    0xf5aae1 tree_range_check_failed(tree_node const*, char const*, int, char const*, tree_code, tree_code)
            [...]/source-gcc/gcc/tree.c:9384
    0x66e201 tree_range_check
            [...]/source-gcc/gcc/tree.h:2979
    0x66e201 tsubst_expr
            [...]/source-gcc/gcc/cp/pt.c:14209
    0x6695e3 tsubst_expr
            [...]/source-gcc/gcc/cp/pt.c:13752
    0x66ac07 tsubst_expr
            [...]/source-gcc/gcc/cp/pt.c:13938
    0x667c41 instantiate_decl(tree_node*, int, bool)
            [...]/source-gcc/gcc/cp/pt.c:20367
    0x6ae386 instantiate_pending_templates(int)
            [...]/source-gcc/gcc/cp/pt.c:20484
    0x6edc3d cp_write_global_declarations()
            [...]/source-gcc/gcc/cp/decl2.c:4456

	gcc/cp/
	* pt.c (tsubst_expr) <OMP_TARGET_UPDATE>: Use
	OMP_TARGET_UPDATE_CLAUSES instead of OMP_CLAUSES.
	gcc/testsuite/
	* g++.dg/gomp/tpl-target-update.C: New file.

From-SVN: r222564