First, run configure with the option `--with-drivers=ALL,display`. Upstream confirmed an error in the build process that keeps the display driver disabled when building a static library, but that driver is needed if you want to use libgs through the wrapper library libspectre. So creating a static library manually from the DLL object files isn't required anymore.
Also a massive update on the patch, mostly to enable real support for `--host` on the configure script (instead of relying on `uname`). Full support for `--build` wasn't added to keep the patch smaller and to not make things more complicated as they already are (for example configure runs itself recursively when CCAUX environment variable was set). ghostscript.mk now builds the needed auxiliary tools in a separate stage (as native binaries) and deletes the unwanted third-party library sources afterwards. This ensures those binaries will run on the build system and keeping the third-party sources on that step will ensure that configuring doesn't fail if i.e. native libjpeg development files aren't found.
Builds on all four MXE targets and the libraries are confirmed to work.
It appears that the default static library created with "make libgs" doesn't always work correctly. I had issues where a postscript viewer would only display the .ps files if it was linked against the shared library (same happened for native Linux builds). Creating the static library manually from the object files that were used to build the dll fixes this issue.
The following script was applied:
sed ':a;/part of MXE.$/{N;s/\n//;ba}' -i $(git grep -l 'part of MXE')
sed 's/\(part of MXE\).*\(See index.html\)/\1. \2/' -i \
$(git grep -l 'part of MXE.*See index.html')
before='This file is part of MXE. See index.html for further information.'
after='This file is part of MXE. See LICENSE.md for licensing information.'
sed "s/$before/$after/" -i $(git grep -l 'part of MXE')
Then git grep 'index.html for further information' revealed two other files.
One of them was patched manually (patch.mk). Makefile has text
"See index.html for further information" unrelated to licensing.
See https://github.com/mxe/mxe/issues/1500#issuecomment-241340792
darealshinji
Mark Brand
Tony Theodore
Viktor Szakats
Boris Nagaev