BuildSystem: Move all userpace libraries under the userspace directory

As the number of libraries is increasing, root directory starts to
expand. This adds better organization for libraries

userspace/libraries/LibC/include/strings.h

@@ -0,0 +1,23 @@
+#ifndef _STRINGS_H
+#define _STRINGS_H 1
+
+// https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/strings.h.html
+
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
+
+#include <bits/types/locale_t.h>
+
+#define __need_size_t
+#include <sys/types.h>
+
+int ffs(int i);
+int strcasecmp(const char* s1, const char* s2);
+int strcasecmp_l(const char* s1, const char* s2, locale_t locale);
+int strncasecmp(const char* s1, const char* s2, size_t n);
+int strncasecmp_l(const char* s1, const char* s2, size_t n, locale_t locale);
+
+__END_DECLS
+
+#endif