version 3.21.3 - Ensure autogen works in non-srcdir builds Only the configure script should be run from the build directory; the rest of the ancillary tools that modify the sources and generate the configure script itself need to be run inside the source directory. - Use AM_DISTCHECK_CONFIGURE_FLAGS DISTCHECK_CONFIGURE_FLAGS is for users and packagers to override distcheck options, while AM_DISTCHECK_CONFIGURE_FLAGS is for the maintainer of the software. https://www.gnu.org/software/automake/manual/automake.html#DISTCHECK_005fCONFIGURE_005fFLAGS