Setting up crossbuild environment from scratch

1) Create fresh ubuntu 14.04 (Trusty Tahr) VM

    http://cdimage.ubuntu.com/daily-live/current/trusty-desktop-amd64.iso

2) Install packages

    $ sudo apt-get update && sudo apt-get upgrade
    $ sudo apt-get install build-essential libgmp-dev libgmp3-dev git cmake m4 \
        libboost-all-dev automake libtool libleveldb-dev yasm unzip lzip libminiupnpc-dev \
        mingw-w64 gcc-mingw-w64 g++-mingw-w64 binutils-mingw-w64

For full Qt client:

    $ sudo apt-get install qtbase5-dev qt5-default

3) Build boost for windows

    $ wget http://downloads.sourceforge.net/project/boost/boost/1.55.0/boost_1_55_0.tar.bz2
    $ tar xjvf boost_1_55_0.tar.bz2
    $ cd boost_1_55_0
    $ ./bootstrap.sh --without-icu
    $ echo "using gcc : mingw32 : x86_64-w64-mingw32-g++ : <rc>x86_64-w64-mingw32-windres <archiver>x86_64-w64-mingw32-ar <ranlib>x86_64-w64-mingw32-ranlib ;" > user-config.jam
    $ sudo ./bjam toolset=gcc address-model=64 target-os=windows variant=release threading=multi threadapi=win32 \
        link=static runtime-link=static --prefix=/usr/x86_64-w64-mingw32 --user-config=user-config.jam \
        --without-mpi --without-python -sNO_BZIP2=1 --layout=tagged install
    $ cd ..

(-Wno-unused-local-typedefs to suppress warnings)

4) Build zlib for windows (required by Qt5)

    $ wget http://zlib.net/zlib-1.2.8.tar.gz
    $ tar xzvf zlib-1.2.8.tar.gz
    $ cd zlib-1.2.8
    $ CC=x86_64-w64-mingw32-gcc AR=x86_64-w64-mingw32-ar RANLIB=x86_64-w64-mingw32-ranlib ./configure --prefix=/usr/x86_64-w64-mingw32 --static
    $ make
    $ sudo make install
    $ cd ..

5) Build Qt5 for windows (not required for headless daemon)

    $ wget http://download.qt-project.org/official_releases/qt/5.2/5.2.1/single/qt-everywhere-opensource-src-5.2.1.tar.gz 
    $ tar xzvf qt-everywhere-opensource-src-5.2.1.tar.gz

Qt5.2.1 has some problems with preprocessor definitions when building with MinGW.

    $ sed -i -e 's/QT_NO_SESSIONMANAGER/__QT_NO_SESSIONMANAGER/g' \
        ~/qt-everywhere-opensource-src-5.2.1/qtbase/src/gui/kernel/qplatformsessionmanager.h \
        ~/qt-everywhere-opensource-src-5.2.1/qtbase/src/gui/kernel/qsessionmanager.h

    $ export INSTALLPREFIX=/usr/x86_64-w64-mingw32
    $ mkdir qt5-w64-build
    $ cd qt5-w64-build
    $ ../qt-everywhere-opensource-src-5.2.1/configure -prefix / -hostprefix $INSTALLPREFIX/host -plugindir /plugins -translationdir /translations \
        -xplatform win32-g++ -device-option CROSS_COMPILE=x86_64-w64-mingw32- -sysroot $INSTALLPREFIX -confirm-license -release -opensource -static -qt-pcre \
        -no-icu -no-glib -no-javascript-jit -no-sql-sqlite -no-nis -no-cups -no-iconv -no-dbus  -nomake examples \
        -no-feature-style-plastique -no-feature-style-cleanlooks -no-feature-style-motif -no-feature-style-cde -no-feature-style-windowsce \
        -no-feature-style-windowsmobile -no-feature-style-s60 -no-pch -no-sql-odbc -no-compile-examples -no-qml-debug -no-sm \
        -skip qtwebkit -skip qtwebkit-examples -skip qtactiveqt -no-openssl -qt-zlib
    $ make
    $ sudo make install
    $ cd ..

(-Wno-strict-overflow -Wno-strict-aliasing -Wno-unused-parameters to suppress warnings)

Patch Qt5.2.1 to work with cmake for static build. Windows uses library naming convention name.lib, MinGW uses libname.a. So we must replace the names:

    $ cd /usr/x86_64-w64-mingw32/lib/cmake
    $ sudo sed -i -e 's/\/\([^\.]*\)\.lib/\/lib\1\.a/g' $(find * -type f)

6) Build leveldb for windows

    $ git clone https://github.com/bitcoin/bitcoin.git
    $ cp bitcoin/src/leveldb ./ -R
    $ cd leveldb
    $ TARGET_OS=NATIVE_WINDOWS CC=x86_64-w64-mingw32-gcc CXX=x86_64-w64-mingw32-g++ AR=x86_64-w64-mingw32-ar \
        make libleveldb.a libmemenv.a
    $ sudo cp include/leveldb /usr/x86_64-w64-mingw32/include/ -R
    $ sudo cp *.a /usr/x86_64-w64-mingw32/lib/
    $ cd ..

7) Build gmp for windows

    $ wget https://gmplib.org/download/gmp/gmp-5.1.3.tar.lz
    $ lzip -d gmp-5.1.3.tar.lz
    $ tar xvf gmp-5.1.3.tar
    $ mkdir gmp-w64-build
    $ cd gmp-w64-build 
    $ ../gmp-5.1.3/configure --host=x86_64-w64-mingw32 --prefix=/usr/x86_64-w64-mingw32
    $ make
    $ sudo make install
    $ cd ..

8) Build miniupnpc for windows

    $ wget http://miniupnp.free.fr/files/download.php?file=miniupnpc-1.9.tar.gz -O miniupnpc-1.9.tar.gz
    $ tar xzvf miniupnpc-1.9.tar.gz
    $ cd miniupnpc-1.9
    $ CC=x86_64-w64-mingw32-gcc AR=x86_64-w64-mingw32-ar CFLAGS="-DSTATICLIB -I/usr/x86_64-w64-mingw32/include" LDFLAGS=-L/usr/x86_64-w64-mingw32/lib \
        make libminiupnpc.a
    $ sudo mkdir /usr/x86_64-w64-mingw32/include/miniupnpc
    $ sudo cp *.h /usr/x86_64-w64-mingw32/include/miniupnpc/
    $ sudo cp libminiupnpc.a /usr/x86_64-w64-mingw32/lib/
    $ cd ..

9) Build cryptopp-5.6.2 for linux and windows

    $ mkdir cryptopp562
    $ cd cryptopp562
    $ wget http://www.cryptopp.com/cryptopp562.zip
    $ unzip cryptopp562.zip

    Linux
    $ make static
    $ sudo mkdir /usr/include/cryptopp
    $ sudo cp *.h /usr/include/cryptopp
    $ sudo cp libcryptopp.a /usr/lib
    $ make clean

    Windows
    $ CXX=x86_64-w64-mingw32-g++ AR=x86_64-w64-mingw32-ar make static
    $ x86_64-w64-mingw32-ranlib libcryptopp.a
    $ sudo mkdir /usr/x86_64-w64-mingw32/include/cryptopp
    $ sudo cp *.h /usr/x86_64-w64-mingw32/include/cryptopp
    $ sudo cp libcryptopp.a /usr/x86_64-w64-mingw32/lib
    $ make clean

    (-Wno-deprecated to suppress warnings)

    $ cd .. 

10) Qt5.2.1 + cmake opengl issue workaround. Qt5GuiConfigExtras.cmake tries to use opengl (glu32). Prevent it from looking for it.

    $ sudo sed -i -e 's/_qt5gui_find_extra_libs(OPENGL/#_qt5gui_find_extra_libs(OPENGL/g' \
        /usr/x86_64-w64-mingw32/lib/cmake/Qt5Gui/Qt5GuiConfigExtras.cmake