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

fusl/src/env/putenv.c

+#include <stdlib.h>
+#include <string.h>
+
+extern char **__environ;
+char **__env_map;
+
+int __putenv(char *s, int a)
+{
+        int i=0, j=0;
+        char *z = strchr(s, '=');
+        char **newenv = 0;
+        char **newmap = 0;
+        static char **oldenv;
+
+        if (!z) return unsetenv(s);
+        if (z==s) return -1;
+        for (; __environ[i] && memcmp(s, __environ[i], z-s+1); i++);
+        if (a) {
+                if (!__env_map) {
+                        __env_map = calloc(2, sizeof(char *));
+                        if (__env_map) __env_map[0] = s;
+                } else {
+                        for (; __env_map[j] && __env_map[j] != __environ[i]; j++);
+                        if (!__env_map[j]) {
+                                newmap = realloc(__env_map, sizeof(char *)*(j+2));
+                                if (newmap) {
+                                        __env_map = newmap;
+                                        __env_map[j] = s;
+                                        __env_map[j+1] = NULL;
+                                }
+                        } else {
+                                free(__env_map[j]);
+                        }
+                }
+        }
+        if (!__environ[i]) {
+                newenv = malloc(sizeof(char *)*(i+2));
+                if (!newenv) {
+                        if (a && __env_map) __env_map[j] = 0;
+                        return -1;
+                }
+                memcpy(newenv, __environ, sizeof(char *)*i);
+                newenv[i] = s;
+                newenv[i+1] = 0;
+                __environ = newenv;
+                free(oldenv);
+                oldenv = __environ;
+        }
+
+        __environ[i] = s;
+        return 0;
+}
+
+int putenv(char *s)
+{
+        return __putenv(s, 0);
+}