Inability to build FreeBSD-current amd64

I have failed in three attempts over the past week to build FreeBSD-current amd64, error message is about the same each time.

Build host uname -a shows

FreeBSD amelia 11.1-STABLE FreeBSD 11.1-STABLE #4: Sun Jul 30 17:28:39 UTC 2017     root_at_amelia2:/usr/obj/BETA1/usr/src11/sys/SANDY11NC  amd64

Is there a known snag?  Would I do better to attempt to build 12-STABLE, or use a FreeBSD-current installation from August 2, 2017 as host?

Snag seems related to llwm, which has been a troublemaker.

Build ends with

===> usr.bin/clang/llvm-mc (all)
Warning: Object directory not changed from original /usr/src/usr.bin/clang/llvm-mc
c++ -target x86_64-unknown-freebsd13.0 --sysroot=/usr/obj/usr/src/amd64.amd64/tmp -B/usr/obj/usr/src/amd64.amd64/tmp/usr/bin -O2 -pipe -I/usr/obj/usr/src/amd64.amd64/lib/clang/libllvm -I/usr/src/lib/clang/include -I/usr/src/contrib/llvm/include -DLLVM_BUILD_GLOBAL_ISEL -D__STDC_LIMIT_MACROS -D__STDC_CONSTANT_MACROS -DLLVM_DEFAULT_TARGET_TRIPLE=\"x86_64-unknown-freebsd13.0\" -DLLVM_HOST_TRIPLE=\"x86_64-unknown-freebsd13.0\" -DDEFAULT_SYSROOT=\"\" -DLLVM_TARGET_ENABLE_AARCH64 -DLLVM_TARGET_ENABLE_ARM -DLLVM_TARGET_ENABLE_MIPS -DLLVM_TARGET_ENABLE_POWERPC -DLLVM_TARGET_ENABLE_SPARC -DLLVM_TARGET_ENABLE_X86 -DLLVM_NATIVE_ASMPARSER=LLVMInitializeX86AsmParser -DLLVM_NATIVE_ASMPRINTER=LLVMInitializeX86AsmPrinter -DLLVM_NATIVE_DISASSEMBLER=LLVMInitializeX86Disassembler -DLLVM_NATIVE_TARGET=LLVMInitializeX86Target -DLLVM_NATIVE_TARGETINFO=LLVMInitializeX86TargetInfo -DLLVM_NATIVE_TARGETMC=LLVMInitializeX86TargetMC -ffunction-sections -fdata-sections -gline-tables-only -fstack-protector-strong
  -Wno-empty-body -Wno-string-plus-int -Wno-unused-const-variable -Wno-tautological-compare -Wno-unused-value -Wno-parentheses-equality -Wno-unused-function -Wno-enum-conversion -Wno-unused-local-typedef -Wno-address-of-packed-member -Wno-switch -Wno-switch-enum -Wno-knr-promoted-parameter -Wno-parentheses -Qunused-arguments -fno-exceptions -fno-rtti -std=c++11 -stdlib=libc++ -Wno-c++11-extensions  -Wl,--gc-sections  -o llvm-mc.full  Disassembler.o llvm-mc.o /usr/obj/usr/src/amd64.amd64/lib/clang/libllvm/libllvm.a  -lz  -lncursesw  -lpthread
objcopy --only-keep-debug llvm-mc.full llvm-mc.debug
objcopy --strip-debug --add-gnu-debuglink=llvm-mc.debug  llvm-mc.full llvm-mc
===> usr.bin/clang/llvm-mca (all)
Warning: Object directory not changed from original /usr/src/usr.bin/clang/llvm-mca
c++  -target x86_64-unknown-freebsd13.0 --sysroot=/usr/obj/usr/src/amd64.amd64/tmp -B/usr/obj/usr/src/amd64.amd64/tmp/usr/bin  -O2 -pipe -I/usr/src/contrib/llvm/tools/llvm-mca -I/usr/obj/usr/src/amd64.amd64/lib/clang/libllvm -I/usr/src/lib/clang/include -I/usr/src/contrib/llvm/include -DLLVM_BUILD_GLOBAL_ISEL -D__STDC_LIMIT_MACROS -D__STDC_CONSTANT_MACROS -DLLVM_DEFAULT_TARGET_TRIPLE=\"x86_64-unknown-freebsd13.0\" -DLLVM_HOST_TRIPLE=\"x86_64-unknown-freebsd13.0\" -DDEFAULT_SYSROOT=\"\" -DLLVM_TARGET_ENABLE_AARCH64 -DLLVM_TARGET_ENABLE_ARM -DLLVM_TARGET_ENABLE_MIPS -DLLVM_TARGET_ENABLE_POWERPC -DLLVM_TARGET_ENABLE_SPARC -DLLVM_TARGET_ENABLE_X86 -DLLVM_NATIVE_ASMPARSER=LLVMInitializeX86AsmParser -DLLVM_NATIVE_ASMPRINTER=LLVMInitializeX86AsmPrinter -DLLVM_NATIVE_DISASSEMBLER=LLVMInitializeX86Disassembler -DLLVM_NATIVE_TARGET=LLVMInitializeX86Target -DLLVM_NATIVE_TARGETINFO=LLVMInitializeX86TargetInfo -DLLVM_NATIVE_TARGETMC=LLVMInitializeX86TargetMC -ffunction-sections -fdata-sections -g
 line-tables-only -MD -MF.depend.Views_DispatchStatistics.o -MTViews/DispatchStatistics.o -fstack-protector-strong -Wno-empty-body -Wno-string-plus-int -Wno-unused-const-variable -Wno-tautological-compare -Wno-unused-value -Wno-parentheses-equality -Wno-unused-function -Wno-enum-conversion -Wno-unused-local-typedef -Wno-address-of-packed-member -Wno-switch -Wno-switch-enum -Wno-knr-promoted-parameter -Wno-parentheses -Qunused-arguments  -fno-exceptions -fno-rtti -std=c++11 -stdlib=libc++ -Wno-c++11-extensions  -c /usr/src/contrib/llvm/tools/llvm-mca/Views/DispatchStatistics.cpp -o Views/DispatchStatistics.o
error: unable to open output file 'Views/DispatchStatistics.o': 'No such file or directory'
1 error generated.
*** Error code 1

Stop.
make[5]: stopped in /usr/src/usr.bin/clang/llvm-mca
*** Error code 1

Stop.
make[4]: stopped in /usr/src/usr.bin/clang
*** Error code 1

Stop.
make[3]: stopped in /usr/src/usr.bin
*** 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


Tom