enable --disable-dependency-tracking on CYGWIN also

[jeremyd2019]

it also takes an inordinate amount of time there.

[jeremyd2019]

As you may have noticed by my pull requests on llvm/llvm-project, I've been playing with clang on Cygwin. I figured it'd be good exercise for it to run ./build-all.sh --host-clang and see what broke. Nothing did, but the dependency tracking stuff took a long time, as it does on MSYS2.

[mstorsjo]

LGTM, thanks! (I amended your patch to spell out your name properly, as it only had the username, not the full name, in the commit.) I'll merge it after letting the CI run for a while (even though I don't foresee it breaking).

[jeremyd2019]

BTW, I was eventually able to use the --host-clang toolchain to then build-cross-tools for i686, but:

1. I gave up on --with-python after several rounds fighting it - upstream cpython doesn't build out-of-the box on Cygwin, and then things went sideways trying to build cpython-mingw, not finding the python import lib.
2. I had to include the Signals patch from [LLVM][Clang][Cygwin] Fix building Clang for Cygwin llvm/llvm-project#134494, and add cmake option -DCROSS_TOOLCHAIN_FLAGS_NATIVE="-DCMAKE_CXX_FLAGS=-D_GNU_SOURCE=1;-DCMAKE_C_FLAGS=-D_GNU_SOURCE=1" so the "NATIVE" tools (llvm-min-tblgen etc) would build.