Added support for dladdr()

dladdr() is a GNU extension function, which allows the caller to retrieve
symbol information for a specified memory address.  It is useful for things
like generating backtrace information at runtime.

Change-Id: I3a1def1a6c9c666d93e1e97b7d260dfa5b9b79a9

libc/include/dlfcn.h

@@ -32,10 +32,22 @@
 
 __BEGIN_DECLS
 
+typedef struct {
+    const char *dli_fname;  /* Pathname of shared object that
+                               contains address */
+    void       *dli_fbase;  /* Address at which shared object
+                               is loaded */
+    const char *dli_sname;  /* Name of nearest symbol with address
+                               lower than addr */
+    void       *dli_saddr;  /* Exact address of symbol named
+                               in dli_sname */
+} Dl_info;
+
 extern void*        dlopen(const char*  filename, int flag);
 extern int          dlclose(void*  handle);
 extern const char*  dlerror(void);
 extern void*        dlsym(void*  handle, const char*  symbol);
+extern int          dladdr(void* addr, Dl_info *info);
 
 enum {
   RTLD_NOW  = 0,