Step-by-step instructions to build Emacs for Windows 64 bit with MSYS2 and MinGW-w64.

Build Emacs-w64 with MSYS2/MinGW-w64

Instructions are modified from emacs-w64 Wiki page by zklhp. Many thanks for sharing!

Download MSYS2 (msys2-x86_64-20161025.exe) from this download page.
Install MSYS2 to, for example, C:\msys2 (make sure no space in path).
Optionally prettify the MSYS2 console mintty with ~/.minttyrc to make it more pleasing to eyes. Thanks to this awesome theme!

ForegroundColour=131,148,150
BackgroundColour=0,43,54
CursorColour=192,192,192
Black=7,54,66
BoldBlack=0,43,54
Red=220,50,47
BoldRed=203,75,22
Green=133,153,0
BoldGreen=88,110,117
Yellow=181,137,0
BoldYellow=101,123,131
Blue=38,139,210
BoldBlue=131,148,150
Magenta=211,54,130
BoldMagenta=108,113,196
Cyan=42,161,152
BoldCyan=147,161,161
White=238,232,213
BoldWhite=253,246,227
BoldAsFont=yes
Font=Consolas
FontHeight=12
Transparency=off
OpaqueWhenFocused=no
ScrollbackLines=200000
FontSmoothing=full
CursorType=underscore
CursorBlinks=yes
ScrollMod=off
RightClickAction=paste
ClickTargetMod=off

Remove all /c/* paths in $PATH by adding this to .bashrc and restart mintty.

This is important to avoid interference from programs installed on the same machine, especially if you have Cygwin installed.

# Remove '/c/*' from PATH if running under Msys to avoid possible 
# interference from programs already installed on system. Removal 
# with awk is copied from http://stackoverflow.com/a/370192.
if [ $(uname -o) == 'Msys' ]; then
    export PATH=`echo ${PATH} | awk -v RS=: -v ORS=: '/c\// {next} {print}' | sed 's/:*$//'`
fi

The whole .bashrc is copied here.

# .bashrc
 
# Source global definitions
if [ -f /etc/bashrc ]; then
    . /etc/bashrc
fi
 
##############
### Basics ###
##############
 
# Don't wait for job termination notification
set -o notify
 
# Enables UTF-8 in Putty.
# See http://www.earth.li/~huggie/blog/tech/mobile/putty-utf-8-trick.html
echo -ne '\e%G\e[?47h\e%G\e[?47l'
 
# My pretty prompt (Yay!)
PS1='\[\e[32;40m\]\u\[\e[0m\]\[\e[34;40m\]\H\[\e[0m\]\[\e[40;1m\]\w\[\e[0m\] '
 
############
### PATH ###
############
 
# Remove '/c/*' from PATH if running under Msys to avoid possible 
# interference from programs already installed on system. Removal 
# with awk is copied from http://stackoverflow.com/a/370192.
if [ $(uname -o) == 'Msys' ]; then
    export PATH=`echo ${PATH} | awk -v RS=: -v ORS=: '/c\// {next} {print}' | sed 's/:*$//'`
fi
 
###############
### Aliases ###
###############
 
 
alias less='less -r'
alias rm='rm -i'
alias whence='type -a'
alias ls='ls -F --color=auto'
alias dir='ls --color=auto --format=long -L'
alias vdir='ls --color=auto --format=long'
alias ll='ls -l'
alias la='ls -A'
alias l='ls -CF'
alias md='mkdir'
alias pico='nano'
alias cls='clear'

Install packages required to build Emacs.

Follow instructions on this page first.

pacman -Syu
pacman -Sy
pacman -Sy\
    --needed \
    filesystem \
    msys2-runtime \
    bash \
    libreadline \
    libiconv \
    libarchive \
    libgpgme \
    libcurl \
    pacman \
    ncurses \
    libintl

Close mintty and restart it, do this again.

pacman -Su

Then let us install all required libs for building Emacs.

#!/usr/bin/bash
pacman -S \
      autoconf \
      autogen \
      automake \
      automake-wrapper \
      diffutils \
      git \
      guile \
      libgc \
      libguile \
      libltdl \
      libunistring \
      make \
      mingw-w64-x86_64-binutils \
      mingw-w64-x86_64-bzip2 \
      mingw-w64-x86_64-cairo \
      mingw-w64-x86_64-cloog \
      mingw-w64-x86_64-crt-git \
      mingw-w64-x86_64-dbus \
      mingw-w64-x86_64-expat \
      mingw-w64-x86_64-fontconfig \
      mingw-w64-x86_64-freetype \
      mingw-w64-x86_64-gcc \
      mingw-w64-x86_64-gcc-libs \
      mingw-w64-x86_64-gdk-pixbuf2 \
      mingw-w64-x86_64-gettext \
      mingw-w64-x86_64-giflib \
      mingw-w64-x86_64-glib2 \
      mingw-w64-x86_64-gmp \
      mingw-w64-x86_64-gnutls \
      mingw-w64-x86_64-harfbuzz \
      mingw-w64-x86_64-headers-git \
      mingw-w64-x86_64-imagemagick \
      mingw-w64-x86_64-isl \
      mingw-w64-x86_64-libcroco \
      mingw-w64-x86_64-libffi \
      mingw-w64-x86_64-libiconv \
      mingw-w64-x86_64-libjpeg-turbo \
      mingw-w64-x86_64-libpng \
      mingw-w64-x86_64-librsvg \
      mingw-w64-x86_64-libtiff \
      mingw-w64-x86_64-libwinpthread-git \
      mingw-w64-x86_64-libxml2 \
      mingw-w64-x86_64-mpc \
      mingw-w64-x86_64-mpfr \
      mingw-w64-x86_64-pango \
      mingw-w64-x86_64-pixman \
      mingw-w64-x86_64-winpthreads \
      mingw-w64-x86_64-xpm-nox \
      mingw-w64-x86_64-xz \
      mingw-w64-x86_64-zlib \
      tar \
      wget

Get emacs source.

mkdir emacs; cd emacs
git clone http://git.savannah.gnu.org/r/emacs.git emacs
git config core.autocrlf false

Build Emacs!

Change target accordingly, the directory in which the freshly built Emacs binaries, libraries, and docs live.

target=/c/emacs

export PATH=/mingw64/bin:$PATH
 
mkdir build; cd build

(cd ../emacs; ./autogen.sh)

export PKG_CONFIG_PATH=/mingw64/lib/pkgconfig

../emacs/configure \
    --host=x86_64-w64-mingw32 \
    --target=x86_64-w64-mingw32 \
    --build=x86_64-w64-mingw32 \
    --with-gnutls \
    --with-imagemagick \
    --with-jpeg \
    --with-png \
    --with-rsvg \
    --with-tiff \
    --with-wide-int \
    --with-xft \
    --with-xml2 \
    --with-xpm \
    'CFLAGS=-I/mingw64/include/noX' \
    prefix=$target
 
make
 
make install prefix=$target
 
cp /mingw64/bin/*.dll $target

et2010/Build Emacs for Windows 64bit.md

Build Emacs-w64 with MSYS2/MinGW-w64