LibC: Deprecate strcpy(), strncpy(), strcat() and strncat() :^)

And also mark strlcpy() and strlcat() with __attribute__((warn_unused_result)).

Since our code is warning-free, this ensures we never misuse those functions.
(Or are very sure about doing it when turning off the warning for a particular
piece of code.)

Libraries/LibC/termcap.cpp

@@ -95,6 +95,11 @@ static void ensure_caps()
     caps->set("li", "25");
 }
 
+// Unfortunately, tgetstr() doesn't accept a size argument for the buffer
+// pointed to by area, so we have to use bare strcpy().
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
+
 char* tgetstr(const char* id, char** area)
 {
     ensure_caps();
@@ -113,6 +118,8 @@ char* tgetstr(const char* id, char** area)
     return nullptr;
 }
 
+#pragma GCC diagnostic pop
+
 int tgetflag(const char* id)
 {
     (void)id;