Cross-compiling Boost:

./boostrap.sh
./b2 -d+2 --with-test --with-locale --with-thread --with-iostreams --with-regex --with-filesystem --with-system --with-program_options threadapi=win32 --layout=system target-os=windows link=static variant=release --with-random cxxflags=-I$HOME/win32/wesnoth-xcompile-sdk/include linkflags=-L$HOME/win32/wesnoth-xcompile-sdk/lib --prefix=$HOME/win32/wesnoth-xcompile-sdk/boost -j8 install

(See #wesnoth-dev 2015-07-21/22)

Cross-compiling Wesnoth:

cd <source tree root>
mkdir <name>

scons -Y .. --option-cache=./.scons-option-cache host=i686-w64-mingw32 openmp=true default_targets=all extra_flags_config='-DBOOST_THREAD_USE_LIB -pipe' extra_flags_release='-O3' prefix=$HOME/win32/wesnoth-xcompile-sdk gtkdir=$HOME/win32/wesnoth-xcompile-sdk gettextdir=$HOME/win32/wesnoth-xcompile-sdk boostdir=$HOME/win32/wesnoth-xcompile-sdk/boost/include boostlibdir=$HOME/win32/wesnoth-xcompile-sdk/boost/lib jobs=8 strict=false ccache=true -j8

(test target will fail to link)
(strict=yes is unusable due to linker warnings about section size mismatches)