Applications which use GPGME currently need to use AM_PATH_GPGME for detecting gpgme's presence. However, when
running the autogen.sh script from a source repository, this macro is missing if GPGME is not present, causing
autoconf itself to fail (even if GPGME support is eventually optional in the configure script).
A workaround is to bundle the AM_PATH_GPGME macro in the project VCS, but this is ugly and hackish.
GPGME should instead provide a .pc file so applications can use PKG_CHECK_MODULES for checking (and be integrated
into other build systems besides Autotools, such as CMake which has pkg-config support).