LibC: Add stub for fnmatch and a set of defined values

This adds a stub for fnmatch and the following defined values:
- FNM_PATHNAME
- FNM_NOESCAPE
- FNM_PERIOD
- FNM_FILE_NAME
- FNM_LEADING_DIR
- FNM_CASEFOLD
- FNM_EXTMATCH

Userland/Libraries/LibC/fnmatch.cpp

@@ -0,0 +1,14 @@
+/*
+ * Copyright (c) 2021, the SerenityOS developers
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/Format.h>
+#include <fnmatch.h>
+
+int fnmatch(char const*, char const*, int)
+{
+    dbgln("FIXME: Implement fnmatch()");
+    return 0;
+}