commit
de90f38e3b105802655d19d965d66335d25d59ef omitted $(srcdir) from
the makefile include pathname it added. since the include directive
was prefixed with - to make it optional (for archs that don't use it),
the failure to find arch/$(ARCH)/arch.mak was silent.
LDSO_PATHNAME = $(syslibdir)/ld-musl-$(ARCH)$(SUBARCH).so.1
-include config.mak
--include arch/$(ARCH)/arch.mak
+-include $(srcdir)/arch/$(ARCH)/arch.mak
ifeq ($(ARCH),)