Problem with buildkernel

After buildworld of yesterday the buildkernel fails with the following message:r/src/tmp/usr/bin -c -O2 -pipe -fno-strict-aliasing -nostdinc -I. -I/usr/src/sys -I/usr/src/sys/contrib/libfdt -D_KERNEL -DHAVE_KERNEL_OPTION_HEADERS -include opt_global.h -MD  -MF.depend.if_hn.o -MTif_hn.o -mno-mmx -mno-sse -msoft-float -ffreestanding -fwrapv -fstack-protector -Wall -Wredundant-decls -Wnested-externs -Wstrict-prototypes -Wmissing-prototypes -Wpointer-arith -Winline -Wcast-qual -Wundef -Wno-pointer-sign -D__printf__=__freebsd_kprintf__ -Wmissing-include-dirs -fdiagnostics-show-option -Wno-unknown-pragmas -Wno-error-tautological-compare -Wno-error-empty-body -Wno-error-parentheses-equality -Wno-error-unused-function -Wno-error-pointer-sign -Wno-error-shift-negative-value -Wno-error-address-of-packed-member -mno-aes -mno-avx -std=iso9899:1999 -Werror /usr/src/sys/dev/hyperv/netvsc/if_hn.c*** Error code 1Stop.make[2]: stopped in /usr/obj/usr/src/sys/STING_VT*** Error code 1Stop.make[1]: stopped in /usr/src*** Error code 1Stop.make: stopped in /usr/src~
[root_at_sting /home/filippo]# uname -aFreeBSD sting 12.0-CURRENT FreeBSD 12.0-CURRENT #4 r322877M: Fri Aug 25 19:11:32 CEST 2017 root_at_sting:/usr/obj/usr/src/sys/STING_VT i386sincerelyFilippo