I noticed recently that Emacs didn't have any build instructions for 64-bit
Windows - I tried the instructions for the 32-bit build in nt/INSTALL last
year [1] but something went wrong at some point (I don't remember what,
exactly). I tried again recently using the instructions from the Emacs-w64
project [2] which uses MSYS2 and MinGW-w64 - it worked well and it was also
easier to get the necessary libraries, as it has a package manager, pacman.

So I thought I would try adapting those instructions to include with Emacs,
if
it would be helpful - the author Chris Zheng said he wouldn't mind, and I
could
post it here or the devlist for feedback - it could go in a separate
INSTALL64
document, if the existing one is too long.

Are there any issues with using MSYS2 over MSYS? I think you can build a
32-bit
Emacs with MSYS2 also, but I'm not sure - if so it would be possible to
cover
both with one document, which might be simpler, but I could start with the
64-bit instructions anyway.

Brian Burns

[1] https://github.com/emacs-mirror/emacs/blob/master/nt/INSTALL
[2]
http://sourceforge.net/p/emacsbinw64/wiki/Build%20guideline%20for%20MSYS2-MinGW-w64%20system/