LibC: Stub and test strlcpy

Author: https://github.com/BenWiederhake
Commit: 3fc2c4866f
Pull-request: https://github.com/SerenityOS/serenity/pull/3275
Reviewed-by: https://github.com/awesomekling

Libraries/LibC/string.h

@@ -48,6 +48,7 @@ void* memset(void*, int, size_t);
 __attribute__((malloc)) char* strdup(const char*);
 __attribute__((malloc)) char* strndup(const char*, size_t);
 char* strcpy(char* dest, const char* src);
+size_t strlcpy(char* dest, const char* src, size_t);
 char* strncpy(char* dest, const char* src, size_t);
 char* strchr(const char*, int c);
 char* strchrnul(const char*, int c);