factor symbol counting out of dladdr as its own function

the fdpic code will need to count symbols, and it may be useful
elsewhere in the future too. counting is trivial as long as sysv hash
is present, but for gnu-hash-only libraries it's complex.

the behavior of the count is changed slightly: we now include symbols
that are not accessible by the gnu hash table in the count. this may
make dladdr slightly slower. if this is a problem, dladdr can subtract
out the part that should not be accessible. unlike in the old code,
subtracting this out is easy even in the fast path where sysv hash is
available too.

src/ldso/dynlink.c

@@ -704,6 +704,25 @@ static void decode_dyn(struct dso *p)
 		p->versym = laddr(p, *dyn);
 }
 
+static size_t count_syms(struct dso *p)
+{
+	if (p->hashtab) return p->hashtab[1];
+
+	size_t nsym, i;
+	uint32_t *buckets = p->ghashtab + 4 + (p->ghashtab[2]*sizeof(size_t)/4);
+	uint32_t *hashval;
+	for (i = nsym = 0; i < p->ghashtab[0]; i++) {
+		if (buckets[i] > nsym)
+			nsym = buckets[i];
+	}
+	if (nsym) {
+		hashval = buckets + p->ghashtab[0] + (nsym - p->ghashtab[1]);
+		do nsym++;
+		while (!(*hashval++ & 1));
+	}
+	return nsym;
+}
+
 static struct dso *load_library(const char *name, struct dso *needed_by)
 {
 	char buf[2*NAME_MAX+2];
@@ -1613,7 +1632,6 @@ int __dladdr(const void *addr, Dl_info *info)
 	Sym *sym;
 	uint32_t nsym;
 	char *strings;
-	size_t i;
 	void *best = 0;
 	char *bestname;
 
@@ -1625,24 +1643,7 @@ int __dladdr(const void *addr, Dl_info *info)
 
 	sym = p->syms;
 	strings = p->strings;
-	if (p->hashtab) {
-		nsym = p->hashtab[1];
-	} else {
-		uint32_t *buckets;
-		uint32_t *hashval;
-		buckets = p->ghashtab + 4 + (p->ghashtab[2]*sizeof(size_t)/4);
-		sym += p->ghashtab[1];
-		for (i = nsym = 0; i < p->ghashtab[0]; i++) {
-			if (buckets[i] > nsym)
-				nsym = buckets[i];
-		}
-		if (nsym) {
-			nsym -= p->ghashtab[1];
-			hashval = buckets + p->ghashtab[0] + nsym;
-			do nsym++;
-			while (!(*hashval++ & 1));
-		}
-	}
+	nsym = count_syms(p);
 
 	for (; nsym; nsym--, sym++) {
 		if (sym->st_value