While packaging cmark-gfm 0.29.0.gfm.2 libraries for build2 toolchain, I have noticed that the public header cmark-gfm-core-extensions.h includes the private header config.h:

#include "config.h" // for bool

Thus building a program that includes cmark-gfm-core-extensions.h against the installed cmark-gfm libraries fails with:

/tmp/install/include/cmark-gfm-core-extensions.h:10:10: fatal error: config.h: No such file or directory