bug#48303: 28.0.50; Build of master fails on MSYS2 MINGW64 environment

[Yasuhiro Kimura]

From: Eli Zaretskii <eliz@gnu.org>
Subject: Re: bug#48303: 28.0.50; Build of master fails on MSYS2 MINGW64 
environment
Date: Sun, 09 May 2021 11:01:35 +0300

>> Date: Sun, 09 May 2021 07:35:09 +0900 (JST)
>> From: Yasuhiro Kimura <yasu@utahime.org>
>> 
>> In file included from w32image.c:32:
>> w32common.h:45:3: error: expected identifier before numeric constant
>>    45 |   OS_NT
>>       |   ^~~~~
>> make[1]: *** [Makefile:385: w32image.o] Error 1
>> make[1]: Leaving directory '/c/Users/yasu/Work/Emacs/master/emacs/src'
>> make: *** [Makefile:425: src] Error 2
> 
> That's because w32 API headers now invade on our enumeration.  Fixed
> on the emacs-27 branch, soon to be merged to master.

Thank for information. I cherry-picked 4c3abb3dd1 of emacs-27 to
af529f777c of master and confirmed build completes successfully. But
after cherry-picking one 'OS_9X' is still left at line 7658 of
src/w32term.c. Right now it is commented out with '#if 0 ... #endif'.
But to make sure it should also be changed to 'OS_SUBTYPE_9X'.