missing: move sys_execveat() to missing.h

The missing.h header provides syscalls potentially missing from the used
libc. Move the sys_execveat() definition into it. It doesn't belong into
vfstest.c.

Acked-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Signed-off-by: Zorro Lang <zlang@kernel.org>
diff --git a/src/vfs/missing.h b/src/vfs/missing.h
index c4f4cc3..059e742 100644
--- a/src/vfs/missing.h
+++ b/src/vfs/missing.h
@@ -148,4 +148,15 @@
 	return syscall(__NR_umount2, path, flags);
 }
 
+static inline int sys_execveat(int fd, const char *path, char **argv,
+			       char **envp, int flags)
+{
+#ifdef __NR_execveat
+	return syscall(__NR_execveat, fd, path, argv, envp, flags);
+#else
+	errno = ENOSYS;
+	return -1;
+#endif
+}
+
 #endif /* __IDMAP_MISSING_H */
diff --git a/src/vfs/vfstest.c b/src/vfs/vfstest.c
index 8a68565..1d71b25 100644
--- a/src/vfs/vfstest.c
+++ b/src/vfs/vfstest.c
@@ -226,17 +226,6 @@
 }
 #endif
 
-static int sys_execveat(int fd, const char *path, char **argv, char **envp,
-			int flags)
-{
-#ifdef __NR_execveat
-	return syscall(__NR_execveat, fd, path, argv, envp, flags);
-#else
-	errno = ENOSYS;
-	return -1;
-#endif
-}
-
 static void test_setup(struct vfstest_info *info)
 {
 	if (mkdirat(info->t_mnt_fd, T_DIR1, 0777))