clang-scan-deps: Pass ${TDFILE} to tblgen, not ${.ALLSRC}

[ivy]

Summary

${.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

[ivy]

noticed running buildworld on a recent main. i'm not exactly sure why this used to work and suddenly stopped working, but the change seems correct.

===> usr.bin/clang/clang-scan-deps (all)
--- Opts.inc ---
llvm-tblgen -gen-opt-parser-defs -I /home/ivy/src/bsd/main/contrib/llvm-project/llvm/include -d Opts.inc.d  -o Opts.inc /home/ivy/src/bsd/main/contrib/llvm-project/clang/tools/clang-scan-deps/Opts.td /home/ivy/src/bsd/main/contrib/llvm-project/llvm/include/llvm/Option/OptParser.td
llvm-tblgen: Too many positional arguments specified!
Can specify at most 1 positional arguments: See: llvm-tblgen --help
*** [Opts.inc] Error code 1

make[5]: stopped making "all" in /home/ivy/src/bsd/main/usr.bin/clang/clang-scan-deps
make[5]: 1 error

[dim]

Yes, this is why ${.ALLSRC} is not always a magic bullet. :)

[ivy]

this worked on my dev worktree, but not when i built it on main since TDFILE
was set wrong. this should fix both issues!