SVN r350713 breaks non-debug kernel builds

[Michael Butler]

As follows ..

--- kern_sysctl.o ---
/usr/src/sys/kern/kern_sysctl.c:1623:19: error: use of undeclared
identifier 'kdb_active'
        if (arg2 == 0 || kdb_active) {
                         ^
1 error generated.
*** [kern_sysctl.o] Error code 1

	imb