LibC+LibELF: Implement dladdr()

This implements the dladdr() function which lets the caller look up
the symbol name, symbol address as well as library name and library
base address for an arbitrary address.

Userland/Libraries/LibDl/dlfcn.cpp

@@ -60,3 +60,15 @@ void* dlsym(void* handle, const char* symbol_name)
     }
     return result.value();
 }
+
+int dladdr(void* addr, Dl_info* info)
+{
+    auto result = __dladdr(addr, info);
+    if (result.is_error()) {
+        // FIXME: According to the man page glibc does _not_ make the error
+        // available via dlerror(), however we do. Does this break anything?
+        store_error(result.error().text);
+        return 0;
+    }
+    return 1;
+}