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/regex.h

@@ -0,0 +1,54 @@
+#ifndef _REGEX_H
+#define _REGEX_H 1
+
+// https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/regex.h.html
+
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
+
+#define __need_size_t
+#include <sys/types.h>
+
+typedef struct
+{
+	size_t re_nsub;
+} regex_t;
+
+typedef __PTRDIFF_TYPE__ regoff_t;
+
+typedef struct
+{
+	regoff_t rm_so;	/* Byte offset from start of string to start of substring. */
+	regoff_t rm_eo;	/* Byte offset from start of string of the first character after the end of substring. */
+} regmatch_t;
+
+#define REG_EXTENDED	0x01
+#define REG_ICASE		0x02
+#define REG_NOSUB		0x04
+#define REG_NEWLINE		0x80
+
+#define REG_NOTBOL		0x0001
+#define REG_NOTEOL		0x0002
+#define REG_NOMATCH		0x0004
+#define REG_BADPAT		0x0008
+#define REG_ECOLLATE	0x0010
+#define REG_ECTYPE		0x0020
+#define REG_EESCAPE		0x0040
+#define REG_ESUBREG		0x0080
+#define REG_EBRACK		0x0100
+#define REG_EPAREN		0x0200
+#define REG_EBRACE		0x0400
+#define REG_BADBR		0x0800
+#define REG_ERANGE		0x1000
+#define REG_ESPACE		0x2000
+#define REG_BADRPT		0x4000
+
+int		regcomp(regex_t* __restrict preg, const char* __restrict pattern, int cflags);
+size_t	regerror(int errcode, const regex_t* __restrict preg, char* __restrict errbuf, size_t errbuf_size);
+int		regexec(const regex_t* __restrict preg, const char* __restrict string, size_t nmatch, regmatch_t pmatch[__restrict], int eflags);
+void	regfree(regex_t* preg);
+
+__END_DECLS
+
+#endif