fix double-processing of DT_RELR relocations in ldso relocating itself

this is analogous to skip_relative logic in do_relocs -- because
relative relocations for the dynamic linker itself were already
performed at entry (stage 1), they must not be applied again.

ldso/dynlink.c

@@ -552,6 +552,7 @@ static void do_relocs(struct dso *dso, size_t *rel, size_t rel_size, size_t stri
 
 static void do_relr_relocs(struct dso *dso, size_t *relr, size_t relr_size)
 {
+	if (dso == &ldso) return; /* self-relocation was done in _dlstart */
 	unsigned char *base = dso->base;
 	size_t *reloc_addr;
 	for (; relr_size; relr++, relr_size-=sizeof(size_t))