While trying to cross-compile luatex from linux to win32 using mingw, I got a
failure due to the --host setting not matching what is installed on my machine.
I changed that in build.sh and got a second, but less serious error, about
mingw32-strip no being found.
I suggest the attached patch to build.sh to make cross-compilation more
configurable. Hopefully, ./build.sh --mingw will continue to work were it used
to, but the platforms will also be configurable with, eg
./build.sh --mingw --host=i586-mingw32msvc --build=x84_64-linux-gnu
This command line works on my platform, but I couldn't test if just --mingw
still works elsewhere, so you may want to test that on your machine.