LibC: Let setlocale() pretend that setting the locale succeeded

By returning nullptr we're telling the caller that setlocale() failed.
Some programs expect setlocale() to succeed so let's pretend that it
did.

Userland/Libraries/LibC/locale.cpp

@@ -7,6 +7,7 @@
 #include <assert.h>
 #include <locale.h>
 #include <stdio.h>
+#include <string.h>
 
 extern "C" {
 
@@ -46,7 +47,9 @@ static struct lconv default_locale = {
 
 char* setlocale(int, const char*)
 {
-    return nullptr;
+    static char locale[2];
+    memcpy(locale, "C", 2);
+    return locale;
 }
 
 struct lconv* localeconv()