Bug 31732: Windows nightly builds are busted

It seems we were a bit too optimistic to pick up FORTIFY_SOURCE support
in mingw-w64 as this breaks our builds. Let's be more conservative and
use what Mozilla is using in their mingw-w64/clang builds.

projects/mingw-w64-clang/config

 # vim: filetype=yaml sw=2
 filename: '[% project %]-[% c("version") %]-[% c("var/build_id") %].tar.gz'
 git_url: https://git.code.sf.net/p/mingw-w64/mingw-w64
-git_hash: 330025c54b85512d54b6960fad07498365c8fee3
+git_hash: 0a1d495478d8ed1a94fc77b9dbb428b7e0372588
 version: '[% c("abbrev") %]'
 llvm_version: 8.0.0
 gpg_keyring: clang.gpg

projects/mingw-w64/config

 # vim: filetype=yaml sw=2
 filename: '[% project %]-[% c("version") %]-[% c("var/build_id") %].tar.gz'
 git_url: https://git.code.sf.net/p/mingw-w64/mingw-w64
-git_hash: 330025c54b85512d54b6960fad07498365c8fee3
+git_hash: 0a1d495478d8ed1a94fc77b9dbb428b7e0372588
 version: '[% c("abbrev") %]'
 var:
   container: