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/string.h

@@ -0,0 +1,54 @@
+#ifndef _STRING_H
+#define _STRING_H 1
+
+// https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/string.h.html
+
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
+
+#include <stddef.h>
+#include <bits/types/locale_t.h>
+
+void*	memccpy(void* __restrict s1, const void* __restrict s2, int c, size_t n);
+void*	memchr(const void* s, int c, size_t n);
+int		memcmp(const void* s1, const void* s2, size_t n);
+void*	memcpy(void* __restrict s1, const void* __restrict s2, size_t n);
+void*	memmove(void* s1, const void* s2, size_t n);
+void*	memset(void* s, int c, size_t n);
+char*	stpcpy(char* __restrict s1, const char* __restrict s2);
+char*	stpncpy(char* __restrict s1, const char* __restrict s2, size_t n);
+char*	strcat(char* __restrict s1, const char* __restrict s2);
+char*	strchr(const char* s, int c);
+char*	strchrnul(const char* s, int c);
+int		strcmp(const char* s1, const char* s2);
+int		strcoll(const char* s1, const char* s2);
+int		strcoll_l(const char* s1, const char* s2, locale_t locale);
+char*	strcpy(char* __restrict s1, const char* __restrict s2);
+size_t	strcspn(const char* s1, const char* s2);
+char*	strdup(const char* s);
+char*	strerror(int errnum);
+char*	strerror_l(int errnum, locale_t locale);
+int		strerror_r(int errnum, char* strerrbuf, size_t buflen);
+size_t	strlen(const char* s);
+char*	strncat(char* __restrict s1, const char* __restrict s2, size_t n);
+int		strncmp(const char* s1, const char* s2, size_t n);
+char*	strncpy(char* __restrict s1, const char* __restrict s2, size_t n);
+char*	strndup(const char* s, size_t n);
+size_t	strnlen(const char* s, size_t maxlen);
+char*	strpbrk(const char* s1, const char* s2);
+char*	strrchr(const char* s, int c);
+char*	strsignal(int signum);
+size_t	strspn(const char* s1, const char* s2);
+char*	strstr(const char* s1, const char* s2);
+char*	strtok(char* __restrict s, const char* __restrict sep);
+char*	strtok_r(char* __restrict s, const char* __restrict sep, char** __restrict state);
+size_t	strxfrm(char* __restrict s1, const char* __restrict s2, size_t n);
+size_t	strxfrm_l(char* __restrict s1, const char* __restrict s2, size_t n, locale_t locale);
+
+const char* strerrorname_np(int error);
+const char* strerrordesc_np(int error);
+
+__END_DECLS
+
+#endif