It's 2018. I'm not sure why I added the 32-bit ones; even the 32-bit
bots build and run on 64-bit Windows. ninja.exe in depot_tools is also a
64-bit binary. I suspect this is because some of the depot_tools bits
use --platform=win32, but that's just the sys.platform string.

Alas, I stupidly named these "win32" way back. Dealing with the rename
is probably more trouble than worth it right now since the build recipes
refer to the name. Something to deal with later. (Regardless we'll want
"win32" to point to 64-bit binaries so that try jobs can test it.)

Also add the missing nasm-win32.exe to .gitignore.

For some reason the 64-bit Yasm binary does not work on the vs2017 CQ
bots, so I've left it alone. Hopefully it should be replaced by NASM
later anyway.

Change-Id: If65ececddbc6526ceebaafbef56eddea8ece58ba
Reviewed-on: https://boringssl-review.googlesource.com/29384
Reviewed-by: Steven Valdez <svaldez@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>