c++: rename tsubst_copy_and_build and tsubst_expr

After the previous patch, we now only have two tsubst entry points for
expression trees: tsubst_copy_and_build and tsubst_expr.  The former
despite its unwieldy name is the main entry point, and the latter is
just a superset of the former that also handles statement trees.  We
could merge them so that we just have tsubst_expr, but it seems natural
to distinguish statement trees from expression trees and to maintain a
separate entry point for them.

To that end, this this patch renames tsubst_copy_and_build to
tsubst_expr, and renames the current tsubst_expr to tsubst_stmt, which
continues to be a superset of the former (which is convenient since
sometimes expression trees appear in statement contexts, e.g. a branch
of an IF_STMT could be NOP_EXPR).  (Making tsubst_stmt disjoint from
tsubst_expr is left as future work if deemed desirable.)

This patch in turn renames suitable existing uses of tsubst_expr (that
expect to take statement trees) to use tsubst_stmt.  Thus untouched
tsubst_expr calls are implicitly strengthened to expect only expression
trees after this patch.  For the tsubst_omp_* routines I opted to rename
all existing uses to ensure no unintended functional change.  This patch
also moves the handling of CO_YIELD_EXPR and CO_AWAIT_EXPR from tsubst_stmt
to tsubst_expr since they're indeed expression trees.

gcc/cp/ChangeLog:

	* cp-lang.cc (objcp_tsubst_copy_and_build): Rename to ...
	(objcp_tsubst_expr): ... this.
	* cp-objcp-common.h (objcp_tsubst_copy_and_build): Rename to ...
	(objcp_tsubst_expr): ... this.
	* cp-tree.h (tsubst_copy_and_build): Remove declaration.
	* init.cc (maybe_instantiate_nsdmi_init): Use tsubst_expr
	instead of tsubst_copy_and_build.
	* pt.cc (expand_integer_pack): Likewise.
	(instantiate_non_dependent_expr_internal): Likewise.
	(instantiate_class_template): Use tsubst_stmt instead of
	tsubst_expr for STATIC_ASSERT.
	(tsubst_function_decl): Adjust tsubst_copy_and_build uses.
	(tsubst_arg_types): Likewise.
	(tsubst_exception_specification): Likewise.
	(tsubst_tree_list): Likewise.
	(tsubst): Likewise.
	(tsubst_name): Likewise.
	(tsubst_omp_clause_decl): Use tsubst_stmt instead of tsubst_expr.
	(tsubst_omp_clauses): Likewise.
	(tsubst_copy_asm_operands): Adjust tsubst_copy_and_build use.
	(tsubst_omp_for_iterator): Use tsubst_stmt instead of tsubst_expr.
	(tsubst_expr): Rename to ...
	(tsubst_stmt): ... this.
	<case CO_YIELD_EXPR, CO_AWAIT_EXPR>: Move to tsubst_expr.
	(tsubst_omp_udr): Use tsubst_stmt instead of tsubst_expr.
	(tsubst_non_call_postfix_expression): Adjust tsubst_copy_and_build
	use.
	(tsubst_lambda_expr): Likewise.  Use tsubst_stmt instead of
	tsubst_expr for the body of a lambda.
	(tsubst_copy_and_build_call_args): Rename to ...
	(tsubst_call_args): ... this.  Adjust tsubst_copy_and_build use.
	(tsubst_copy_and_build): Rename to tsubst_expr.  Adjust
	tsubst_copy_and_build and tsubst_copy_and_build_call_args use.
	<case TRANSACTION_EXPR>: Use tsubst_stmt instead of tsubst_expr.
	(maybe_instantiate_noexcept): Adjust tsubst_copy_and_build use.
	(instantiate_body): Use tsubst_stmt instead of tsubst_expr for
	substituting the function body.
	(tsubst_initializer_list): Adjust tsubst_copy_and_build use.

gcc/objcp/ChangeLog:

	* objcp-lang.cc (objcp_tsubst_copy_and_build): Rename to ...
	(objcp_tsubst_expr): ... this.  Adjust tsubst_copy_and_build
	uses.

Reviewed-by: Jason Merrill <jason@redhat.com>