make buildworld error while compiling 12.0-releng for RPI2

[Victor]

I'm trying to compile release 12.0 (with 4 CPUs) on my raspberry pi 2 on which 11.2-RELEASE is installed.
Via svnlite I downloaded the source code under /usr/src and then I started, as the handbook says

make -j4 buildworld

But, unfortunately it spos with the following error:

===> lib/clang/libclang (install)

===> lib/clang/headers (install)
sh /usr/src/tools/install.sh  -C -o root -g wheel -m 444  /usr/src/contrib/llvm/tools/clang/lib/Headers/__clang_cuda_builtin_vars.h ....................................................
c++ -O -pipe -mlong-calls -I/usr/obj/usr/src/arm.armv6/tmp/obj-tools/lib/clang/libclang -I/usr/obj/usr/src/arm.armv6/tmp/obj-tools/lib/clang/libllvm -I/usr/src/contrib/llvm/tools/clang/include -I/usr/src/lib/clang/include -I/usr/src/contrib/llvm/include -DLLVM_BUILD_GLOBAL_ISEL -D__STDC_LIMIT_MACROS -D__STDC_CONSTANT_MACROS -DNDEBUG -DLLVM_DEFAULT_TARGET_TRIPLE=\"armv6-unknown-freebsd12.0-gnueabihf\" -DLLVM_HOST_TRIPLE=\"armv6-unknown-freebsd12.0\" -DDEFAULT_SYSROOT=\"/usr/obj/usr/src/arm.armv6/tmp\" -DLLVM_TARGET_ENABLE_ARM -DLLVM_NATIVE_ASMPARSER=LLVMInitializeARMAsmParser -DLLVM_NATIVE_ASMPRINTER=LLVMInitializeARMAsmPrinter -DLLVM_NATIVE_DISASSEMBLER=LLVMInitializeARMDisassembler -DLLVM_NATIVE_TARGET=LLVMInitializeARMTarget -DLLVM_NATIVE_TARGETINFO=LLVMInitializeARMTargetInfo -DLLVM_NATIVE_TARGETMC=LLVMInitializeARMTargetMC -ffunction-sections -fdata-sections -gline-tables-only -Qunused-arguments -I/usr/obj/usr/src/arm.armv6/tmp/legacy/usr/include -std=c++11 -fno-exceptions -fno-rtti -stdlib=libc++ -Wno-c++11-extensions  -Wl,--gc-sections -static  -L/usr/obj/usr/src/arm.armv6/tmp/legacy/usr/lib -o clang.full  cc1_main.o cc1as_main.o driver.o /usr/obj/usr/src/arm.armv6/tmp/obj-tools/lib/clang/libclang/libclang.a /usr/obj/usr/src/arm.armv6/tmp/obj-tools/lib/clang/libllvm/libllvm.a -L/usr/obj/usr/src/arm.armv6/tmp/obj-tools/lib/libz -lz -L/usr/obj/usr/src/arm.armv6/tmp/obj-tools/lib/ncurses/ncursesw -lncursesw -L/usr/obj/usr/src/arm.armv6/tmp/obj-tools/lib/libthr -lpthread -legacy
c++: error: unable to execute command: Killed
c++: error: linker command failed due to signal (use -v to see invocation)
*** Error code 254
Stop.
make[4]: stopped in /usr/src/usr.bin/clang/clang
*** Error code 1
Stop.
make[3]: stopped in /usr/src/usr.bin/clang
*** Error code 1
Stop.
make[2]: stopped in /usr/src
*** Error code 1
Stop.
make[1]: stopped in /usr/src
*** Error code 1
Stop.
make: stopped in /usr/src


I don't understand this error. What should I do?