depends: Fix id_string invocations

We now use a script named gen_id to generate the base build_id/host_id.
This solves 2 problems:

1. GNU Make special-casing exit code 127 (command not found) meant that
   warnings about missing tools would propagate to the user's terminal
   and broke our opportunistic build_id construction.
2. This change ensures that we don't have arbitrary characters in our
   make variables that would be misinterpreted by Make.

See comments in depends/Makefile and depends/gen_id for more
information.

depends/funcs.mk

@@ -49,7 +49,7 @@ define int_get_build_id
 $(eval $(1)_dependencies += $($(1)_$(host_arch)_$(host_os)_dependencies) $($(1)_$(host_os)_dependencies))
 $(eval $(1)_all_dependencies:=$(call int_get_all_dependencies,$(1),$($($(1)_type)_native_toolchain) $($($(1)_type)_native_binutils) $($(1)_dependencies)))
 $(foreach dep,$($(1)_all_dependencies),$(eval $(1)_build_id_deps+=$(dep)-$($(dep)_version)-$($(dep)_recipe_hash)))
-$(eval $(1)_build_id_long:=$(1)-$($(1)_version)-$($(1)_recipe_hash)-$(release_type) $($(1)_build_id_deps) $($($(1)_type)_id_string))
+$(eval $(1)_build_id_long:=$(1)-$($(1)_version)-$($(1)_recipe_hash)-$(release_type) $($(1)_build_id_deps) $($($(1)_type)_id))
 $(eval $(1)_build_id:=$(shell echo -n "$($(1)_build_id_long)" | $(build_SHA256SUM) | cut -c-$(HASH_LENGTH)))
 final_build_id_long+=$($(package)_build_id_long)