This reverts commit 93f0bcb649087b5db5cfcba5de5faaaf59047751.

This is not correct (from #mingw-w64 IRC):

<andrewrk> is there no .def file for ntdll on arm 64 bit?
<andrewrk> or does mingw-w64-crt/lib64/ntdll.def apply to both x86_64
and aarch64?
<wbs> andrewrk: there's none at the moment (as apps rarely link directly
against ntdll, and I didn't want to guess needlessly around that one
originally when I added arm64 support, before I actually had a real
arm64 windows device)
<wbs> andrewrk: but I guess I could/should complete that now
<wbs> (if you need one right now, the libarm32 one probably is the
closest match)