build: Add conditional use of GPGME
build: Add conditional use of GPGME

Allow to disable GPGME support with option "--without-gpgme" for
configure.

Signed-off-by: Denis Pynkin <denis.pynkin@collabora.com>

Closes: #1889
Approved by: cgwalters

GNOME/ostree,GNOME/ostree,GNOME/ostree,GNOME/ostree,GNOME/ostree