build: fix build failure in --enable-single-binary mode

build: fix build failure in --enable-single-binary mode

* src/local.mk: Avoid overriding automake generated DEPENDENCIES,
so that it applies its adjustments to LDADD to avoid propagating
flags (like -Wl,-rpath) into make targets.  This was seen on FreeBSD
where LIBINTL is set to:
/usr/local/lib/libintl.so -Wl,-rpath -Wl,/usr/local/lib
Instead let automake generate a sanitized src_coreutils_DEPENDENCIES
(based on LDADD), which we then augment with the EXTRA_... variable.