error building clang in HEAD

There is a strange error building clang with this use case:

cd /usr/src
make -j10 makeworld

which produces this error output:

===> lib/clang/libclang (all)
error: unable to rename temporary 'Sema/SemaTemplate-12ad7e30.o.tmp' to output file 'Sema/SemaTemplate.o': 'No such file or directory'
1 error generated.
--- Sema/SemaTemplate.o ---
*** [Sema/SemaTemplate.o] Error code 1

make[6]: stopped in /usr/src/lib/clang/libclang
.ERROR_TARGET='Sema/SemaTemplate.o'
.ERROR_META_FILE='/usr/obj/usr/src/amd64.amd64/lib/clang/libclang/Sema_SemaTemplate.o.meta'
.MAKE.LEVEL='6'
MAKEFILE=''
.MAKE.MODE='meta missing-filemon=yes missing-meta=yes silent=yes'
_ERROR_CMD='c++  -target x86_64-unknown-freebsd12.0 --sysroot=/usr/obj/usr/src/amd64.amd64/tmp -B/usr/obj/usr/src/amd64.amd64/tmp/usr/bin  -O2 -pipe -DNO_MALLOC_EXTRAS -I/usr/obj/usr/src/amd64.amd64/lib/clang/libclang -I/usr/obj/usr/src/amd64.amd64/lib/clang/libllvm -I/usr/src/contrib/llvm/tools/clang/lib/Basic -I/usr/src/contrib/llvm/tools/clang/lib/Driver -I/usr/src/contrib/llvm/tools/clang/include -DCLANG_ENABLE_ARCMT -DCLANG_ENABLE_STATIC_ANALYZER -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-freebsd12.0\" -DLLVM_HOST_TRIPLE=\"x86_64-unknown-freebsd12.0\" -DDEFAULT_SYSROOT=\"\" -DLLVM_TARGET_ENABLE_X86 -DLLVM_NATIVE_ASMPARSER=LLVMInitializeX86AsmParser -DLLVM_NATIVE_ASMPRINTER=LLVMInitializeX86AsmPrinter -DLLVM_NATIVE_DISASSEMBLER=LLVMInitializeX86Disassembler -DLLVM_NATIVE_TARGET=LLVMInitializeX86Target -DLLVM_NATIVE_TARGETINFO=LLVMInitializeX86Tar
 getInfo -DLLVM_NATIVE_TARGETMC=LLVMInitializeX86TargetMC -ffunction-sections -fdata-sections -Qunused-arguments -DNO_MALLOC_EXTRAS  -std=c++11 -fno-exceptions -fno-rtti -stdlib=libc++ -Wno-c++11-extensions  -c /usr/src/contrib/llvm/tools/clang/lib/Sema/SemaTemplate.cpp -o Sema/SemaTemplate.o;'
.CURDIR='/usr/src/lib/clang/libclang'
.MAKE='make'
.OBJDIR='/usr/obj/usr/src/amd64.amd64/lib/clang/libclang'
.TARGETS='all'
DESTDIR='/usr/obj/usr/src/amd64.amd64/tmp'
LD_LIBRARY_PATH=''
MACHINE='amd64'
MACHINE_ARCH='amd64'
MAKEOBJDIRPREFIX=''
MAKESYSPATH='/usr/src/share/mk'
MAKE_VERSION='20180512'
PATH='/usr/obj/usr/src/amd64.amd64/tmp/legacy/usr/sbin:/usr/obj/usr/src/amd64.amd64/tmp/legacy/usr/bin:/usr/obj/usr/src/amd64.amd64/tmp/legacy/bin:/usr/obj/usr/src/amd64.amd64/tmp/usr/sbin:/usr/obj/usr/src/amd64.amd64/tmp/usr/bin:/sbin:/bin:/usr/sbin:/usr/bin'
SRCTOP='/usr/src'
OBJTOP='/usr/obj/usr/src/amd64.amd64'
.MAKE.MAKEFILES='/usr/src/share/mk/sys.mk /usr/src/share/mk/local.sys.env.mk /usr/src/share/mk/src.sys.env.mk /etc/src-env.conf /usr/src/share/mk/bsd.mkopt.mk /usr/src/share/mk/src.sys.obj.mk /usr/src/share/mk/auto.obj.mk /usr/src/share/mk/bsd.suffixes.mk /etc/make.conf /usr/src/share/mk/local.sys.mk /usr/src/share/mk/src.sys.mk /etc/src.conf /usr/src/lib/clang/libclang/Makefile /usr/src/share/mk/src.opts.mk /usr/src/share/mk/bsd.own.mk /usr/src/share/mk/bsd.opts.mk /usr/src/share/mk/bsd.cpu.mk /usr/src/share/mk/bsd.compiler.mk /usr/src/share/mk/bsd.linker.mk /usr/src/lib/clang/clang.pre.mk /usr/src/lib/clang/llvm.pre.mk /usr/src/lib/clang/clang.build.mk /usr/src/lib/clang/llvm.build.mk /usr/src/share/mk/bsd.lib.mk /usr/src/share/mk/bsd.init.mk /usr/src/share/mk/local.init.mk /usr/src/share/mk/src.init.mk /usr/src/lib/clang/libclang/../Makefile.inc /usr/src/share/mk/bsd.libnames.mk /usr/src/share/mk/src.libnames.mk /usr/src/share/mk/bsd.symver.mk /usr/src/share/mk/bsd.nls.mk /usr/src
 /share/mk/bsd.files.mk /usr/src/share/mk/bsd.incs.mk /usr/src/share/mk/bsd.confs.mk /usr/src/share/mk/bsd.links.mk /usr/src/share/mk/bsd.dep.mk /usr/src/share/mk/bsd.clang-analyze.mk /usr/src/share/mk/bsd.obj.mk /usr/src/share/mk/bsd.subdir.mk /usr/src/share/mk/bsd.sys.mk'
.PATH='. /usr/src/lib/clang/libclang /usr/src/contrib/llvm/tools/clang/lib'
1 error

However, if I do this

cd /usr/src/lib/clang/libclang
make -j10 depend all

it succeeds.

I have META_MODE enabled.

It also succeeds with a simple make buildworld, but that's extremely
slow.

Note that this started happening after rm -rf /usr/obj/usr.

-- 
Gary Jennejohn