d: Add convenient overload for build_libcall

d: Add convenient overload for build_libcall

Most generated calls to build_libcall don't require any special
conversions from the generic type returned by the library. Add an
overload that calls the library function without doing any nop casts.

gcc/d/ChangeLog:

	* d-tree.h (build_libcall): New declaration.
	* runtime.cc (build_libcall_1): New function.
	(build_libcall): New overload.
	* d-codegen.cc (build_assert_call): Call build_libcall without Type
	argument.
	(build_array_bounds_call): Likewise.
	(build_bounds_index_condition): Likewise.
	(build_bounds_slice_condition): Likewise.
	(build_closure): Likewise.
	* expr.cc (ExprVisitor::visit): Likewise.
	* toir.cc (IRVisitor::visit): Likewise.