The log for the failure contained errors like this:
```
In file included from ${SRCTOP}/sys/mips/nlm/dev/net/xlpge.c:34:
In file included from ${SRCTOP}/sys/sys/systm.h:44:
In file included from ./machine/atomic.h:849:
${SRCTOP}/sys/sys/_atomic_subword.h:222:37: error: unknown type name 'u_long'; did you mean 'long'?
atomic_testandset_acq_long(volatile u_long *p, u_int v)
^~~~~~
long
```
And similar "unknown type name" errors for u_int, not recognizing bool as a type, etc.
Clearly, <sys/types.h> was missing.