The NetBSD-current/i386 build is working again. The following commits were made between the last failed build and the successful build:
2018.06.04.19.53.01 reinoud src/sys/arch/usermode/include/thunk.h,v 1.65 2018.06.04.19.53.01 reinoud src/sys/arch/usermode/usermode/thunk.c,v 1.90 2018.06.04.20.06.52 reinoud src/sys/arch/usermode/dev/ld_thunkbus.c,v 1.33 2018.06.04.20.12.45 kre src/external/cddl/osnet/dev/dtrace/i386/dtrace_subr.c,v 1.10 2018.06.04.20.28.44 christos src/sys/arch/i386/conf/Makefile.i386,v 1.192 Log files can be found at: http://releng.NetBSD.org/b5reports/i386/commits-2018.06.html#2018.06.04.20.28.44