Make use of ZFS_DEBUG consistent within kmod sources

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes #10623

include/os/freebsd/spl/sys/ccompile.h

@@ -119,9 +119,11 @@ extern "C" {
 #define	__CONST			__sun_attr__((__const__))
 #define	__PURE			__sun_attr__((__pure__))
 
-#if (defined(ZFS_DEBUG) || !defined(NDEBUG))&& !defined(DEBUG)
-#define	DEBUG
+#ifdef INVARIANTS
+#define	ZFS_DEBUG
+#undef 	NDEBUG
 #endif
+
 #define	EXPORT_SYMBOL(x)
 #define	MODULE_AUTHOR(s)
 #define	MODULE_DESCRIPTION(s)
@@ -134,6 +136,9 @@ extern "C" {
 #ifdef ZFS_DEBUG
 #undef NDEBUG
 #endif
+#if !defined(ZFS_DEBUG) && !defined(NDEBUG)
+#define	NDEBUG
+#endif
 
 #ifndef EINTEGRITY
 #define	EINTEGRITY 97 /* EINTEGRITY is new in 13 */