Mark COVERAGE and KCOV as part of KCSAN

While not strictly true this stops them from trying to use the KCSAN atomic
hooks and allows these to be compiled into the same kernel.

Sponsored by:	Innovate UK

sys/kern/kern_kcov.c

@@ -35,6 +35,8 @@
  * $FreeBSD$
  */
 
+#define	KCSAN_RUNTIME
+
 #include <sys/cdefs.h>
 __FBSDID("$FreeBSD$");
 

sys/kern/subr_coverage.c

@@ -35,6 +35,8 @@
  * $FreeBSD$
  */
 
+#define	KCSAN_RUNTIME
+
 #include <sys/cdefs.h>
 __FBSDID("$FreeBSD$");