[Bug d/99794] libphobos: Support building on *-*mingw*

[nightstrike at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99794

nightstrike <nightstrike at gmail dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |nightstrike at gmail dot com

--- Comment #2 from nightstrike <nightstrike at gmail dot com> ---
Hoping this can be backported to 11 so that we can easily bootstrap later
versions.  Meanwhile, will this also fix the build errors on cygwin, or if is
specific to mingw?