Make CONFIG_PREEMPT Fatal

Until support is added for preemptible kernels detect this at
configure time and make it fatal.  Otherwise, it is possible to
have a successful build and kernel modules with flakey behavior.

config/spl-build.m4

@@ -8,6 +8,7 @@
 
 AC_DEFUN([SPL_AC_CONFIG_KERNEL], [
 	SPL_AC_KERNEL
+	SPL_AC_KERNEL_CONFIG
 
 	if test "${LINUX_OBJ}" != "${LINUX}"; then
 		KERNELMAKE_PARAMS="$KERNELMAKE_PARAMS O=$LINUX_OBJ"
@@ -190,6 +191,13 @@ AC_DEFUN([SPL_AC_KERNEL], [
 	SPL_AC_MODULE_SYMVERS
 ])
 
+AC_DEFUN([SPL_AC_KERNEL_CONFIG], [
+	SPL_LINUX_CONFIG([PREEMPT],
+		AC_MSG_ERROR([
+		*** Kernel built with CONFIG_PREEMPT which is not supported.
+		** You must rebuild your kernel without this option.]), [])
+])
+
 dnl #
 dnl # Explicitly check for gawk, we require it for the the usermode
 dnl # helper.  For some reason the standard awk command does not