The NetBSD-current/i386 build is working again. The following commits were made between the last failed build and the successful build:
2018.05.22.09.25.58 maxv src/sys/arch/x86/x86/spectre.c,v 1.14 2018.05.22.09.25.58 maxv src/sys/arch/x86/x86/x86_machdep.c,v 1.115 2018.05.22.10.20.04 maxv src/sys/arch/x86/include/specialreg.h,v 1.123 2018.05.22.10.20.04 maxv src/sys/arch/x86/x86/spectre.c,v 1.15 Log files can be found at: http://releng.NetBSD.org/b5reports/i386/commits-2018.05.html#2018.05.22.10.20.04