Adding "options DEBUG" to a GENERIC kernel produces the following on 
vax.  Things were OK on amd64; I did not test other platforms.  This is 
-current from yesterday.

--- subr_debug.o ---
/usr/src/src-current/sys/kern/subr_debug.c: In function 'freecheck_out':
/usr/src/src-current/sys/kern/subr_debug.c:108: error: 'struct cpu_info' 
has no member named 'ci_ipimsgs'
/usr/src/src-current/sys/kern/subr_debug.c:108: error: 'IPI_SEND_CNCHAR' 
undeclared (first use in this function)
/usr/src/src-current/sys/kern/subr_debug.c:108: error: (Each undeclared 
identifier is reported only once
/usr/src/src-current/sys/kern/subr_debug.c:108: error: for each function 
it appears in.)
/usr/src/src-current/sys/kern/subr_debug.c:108: error: 'IPI_DDB' 
undeclared (first use in this function)
cc1: warnings being treated as errors
/usr/src/src-current/sys/kern/subr_debug.c:108: warning: implicit 
declaration of function 'cpu_handle_ipi'
/usr/src/src-current/sys/kern/subr_debug.c: In function 'freecheck_in':
/usr/src/src-current/sys/kern/subr_debug.c:135: error: 'struct cpu_info' 
has no member named 'ci_ipimsgs'
/usr/src/src-current/sys/kern/subr_debug.c:135: error: 'IPI_SEND_CNCHAR' 
undeclared (first use in this function)
/usr/src/src-current/sys/kern/subr_debug.c:135: error: 'IPI_DDB' 
undeclared (first use in this function)

-Henry Bent