Add a "fork" of musl as //fusl.

fusl/include/regex.h

+#ifndef _REGEX_H
+#define _REGEX_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <features.h>
+
+#define __NEED_regoff_t
+#define __NEED_size_t
+
+#include <bits/alltypes.h>
+
+typedef struct re_pattern_buffer {
+        size_t re_nsub;
+        void *__opaque, *__padding[4];
+        size_t __nsub2;
+        char __padding2;
+} regex_t;
+
+typedef struct {
+        regoff_t rm_so;
+        regoff_t rm_eo;
+} regmatch_t;
+
+#define REG_EXTENDED    1
+#define REG_ICASE       2
+#define REG_NEWLINE     4
+#define REG_NOSUB       8
+
+#define REG_NOTBOL      1
+#define REG_NOTEOL      2
+
+#define REG_OK          0
+#define REG_NOMATCH     1
+#define REG_BADPAT      2
+#define REG_ECOLLATE    3
+#define REG_ECTYPE      4
+#define REG_EESCAPE     5
+#define REG_ESUBREG     6
+#define REG_EBRACK      7
+#define REG_EPAREN      8
+#define REG_EBRACE      9
+#define REG_BADBR       10
+#define REG_ERANGE      11
+#define REG_ESPACE      12
+#define REG_BADRPT      13
+
+#define REG_ENOSYS      -1
+
+int regcomp(regex_t *__restrict, const char *__restrict, int);
+int regexec(const regex_t *__restrict, const char *__restrict, size_t, regmatch_t *__restrict, int);
+void regfree(regex_t *);
+
+size_t regerror(int, const regex_t *__restrict, char *__restrict, size_t);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif