disable legacy init/fini processing on ARM

since the old, poorly-thought-out musl approach to init/fini arrays on
ARM (when it was the only arch that needed them) was to put the code
in crti/crtn and have the legacy _init/_fini code run the arrays,
adding proper init/fini array support caused the arrays to get
processed twice on ARM. I'm not sure skipping legacy init/fini
processing is the best solution to the problem, but it works, and it
shouldn't break anything since the legacy init/fini system was never
used for ARM EABI.

arch/arm/reloc.h

@@ -52,3 +52,5 @@ static inline void do_single_reloc(
 		break;
 	}
 }
+
+#define NO_LEGACY_INITFINI

src/ldso/dynlink.c

@@ -702,8 +702,10 @@ static void do_fini()
 			size_t *fn = (size_t *)(p->base + dyn[DT_FINI_ARRAY])+n;
 			while (n--) ((void (*)(void))*--fn)();
 		}
+#ifndef NO_LEGACY_INITFINI
 		if (dyn[0] & (1<<DT_FINI))
 			((void (*)(void))(p->base + dyn[DT_FINI]))();
+#endif
 	}
 }
 
@@ -723,8 +725,10 @@ static void do_init_fini(struct dso *p)
 			p->fini_next = fini_head;
 			fini_head = p;
 		}
+#ifndef NO_LEGACY_INITFINI
 		if (dyn[0] & (1<<DT_INIT))
 			((void (*)(void))(p->base + dyn[DT_INIT]))();
+#endif
 		if (dyn[0] & (1<<DT_INIT_ARRAY)) {
 			size_t n = dyn[DT_INIT_ARRAYSZ]/sizeof(size_t);
 			size_t *fn = (void *)(p->base + dyn[DT_INIT_ARRAY]);