const-qualify the address argument to dladdr

this agrees with implementation practice on glibc and BSD systems, and
is the const-correct way to do things; it eliminates warnings from
passing pointers to const. the prototype without const came from
seemingly erroneous man pages.

include/dlfcn.h

@@ -31,7 +31,7 @@ typedef struct {
 	const char *dli_sname;
 	void *dli_saddr;
 } Dl_info;
-int dladdr(void *, Dl_info *);
+int dladdr(const void *, Dl_info *);
 int dlinfo(void *, int, void *);
 #endif