autoconf: Fail when __copy_from_user_inatomic is a non-GPL symbol

A followup to 849c14e
Fix https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1009242

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: szubersk <szuberskidamian@gmail.com>
Closes #13389

config/kernel-copy-from-user-inatomic.m4

@@ -18,9 +18,12 @@ AC_DEFUN([ZFS_AC_KERNEL___COPY_FROM_USER_INATOMIC], [
 	AC_MSG_CHECKING([whether __copy_from_user_inatomic is available])
 	ZFS_LINUX_TEST_RESULT([__copy_from_user_inatomic_license], [
 		AC_MSG_RESULT(yes)
-		AC_DEFINE(HAVE___COPY_FROM_USER_INATOMIC, 1,
-		    [__copy_from_user_inatomic is available])
 	], [
 		AC_MSG_RESULT(no)
+		AC_MSG_ERROR([
+	*** The `__copy_from_user_inatomic()` Linux kernel function is
+	*** incompatible with the CDDL license and will prevent the module
+	*** linking stage from succeeding.  OpenZFS cannot be compiled.
+		])
 	])
 ])

module/os/linux/zfs/zfs_uio.c

@@ -75,7 +75,6 @@ zfs_uiomove_iov(void *p, size_t n, zfs_uio_rw_t rw, zfs_uio_t *uio)
 			} else {
 				unsigned long b_left = 0;
 				if (uio->uio_fault_disable) {
-#if defined(HAVE___COPY_FROM_USER_INATOMIC)
 					if (!zfs_access_ok(VERIFY_READ,
 					    (iov->iov_base + skip), cnt)) {
 						return (EFAULT);
@@ -85,9 +84,6 @@ zfs_uiomove_iov(void *p, size_t n, zfs_uio_rw_t rw, zfs_uio_t *uio)
 					    __copy_from_user_inatomic(p,
 					    (iov->iov_base + skip), cnt);
 					pagefault_enable();
-#else
-					return (EFAULT);
-#endif
 				} else {
 					b_left =
 					    copy_from_user(p,