cygwin requirements: in addition to basic abuild requirements, need
ghostscript and tiff utils in order to run image comparison tests.
However, they may not work anyway.  (As of this writing, ghostscript
chokes on some of the files; haven't investigated.)  export
SKIP_TEST_COMPARE_IMAGES=1 to avoid running them.

Must add libqpdf/build to PATH.

To debug a crash in MSVC's debugger, start an instance of Visual C++.
When the abort/retry/ignore dialog pops up, first attach the process
from within visual C++, and then click Retry.

Basic procedure for building with mingw is to run configure and build
in msys and then run the test suite in cygwin with GENDEPS=0.

Also have to deal with gcc runtime DLL.