user: implement mlibc as the libc, finally.

It's finally done..

Signed-off-by: kaguya <vpshinomiya@protonmail.com>

user/include/mlibc/tests/posix/posix_spawn.c

@@ -0,0 +1,38 @@
+#include <stdlib.h>
+#include <assert.h>
+#include <stdio.h>
+#include <string.h>
+
+#include <unistd.h>
+#include <spawn.h>
+#include <sys/wait.h>
+
+extern char **environ;
+
+void run_cmd(char *cmd)
+{
+    pid_t pid;
+    char *argv[] = {"sh", "-c", cmd, NULL};
+    int status;
+    printf("Run command: %s\n", cmd);
+    status = posix_spawn(&pid, "/bin/sh", NULL, NULL, argv, environ);
+    if(status == 0) {
+        printf("Child pid: %i\n", pid);
+        if(waitpid(pid, &status, 0) != -1) {
+            printf("Child exited with status %i\n", status);
+        printf("Child exit status: %i\n", WEXITSTATUS(status));
+        assert(WEXITSTATUS(status) == 0);
+        } else {
+            perror("waitpid");
+        assert(0 == 1);
+        }
+    } else {
+        printf("posix_spawn: %s\n", strerror(status));
+    assert(0 == 1);
+    }
+}
+
+int main() {
+    run_cmd(":");
+    return 0;
+}