${.ALLSRC} can include the dependency OptParser.td, which causes
llvm-tblgen to fail since it only accepts a single input argument.
Use ${TDFILE} directly instead, which matches the other invocations
of tblgen in the LLVM Makefiles.
Fixes: d3c06bed2c16 ("clang: install clang-scan-deps")
MFC after: 3 days