Automatically use the right CFLAGS and LDFLAGS for gpgme
Automatically use the right CFLAGS and LDFLAGS for gpgme

On macOS, (brew install gpgme) installs it within /usr/local, but
/usr/local/include is not in the default search path.

Rather than hard-code this directory, use gpgme-config. Sadly that
must be done at the top-level user instead of locally in the gpgme
subpackage, because cgo supports only pkg-config, not general shell
scripts, and gpgme does not install a pkg-config file.

If gpgme is not installed or gpgme-config can’t be found for other reasons,
the error is silently ignored (and the user will probably find out because
the cgo compilation will fail); this is so that users can use the
containers_image_openpgp build tag without seeing ugly errors
(and without the Makefile having to detect that build tag in even more
shell scripts).

Note that users of this library will probably need a similar modification
to their build environment; we can't do it for them, just as the gpgme
package can't do it for us.

Signed-off-by: Miloslav Trmač <9c008e38982a5397deb855345fb164f0558459ae@redhat.com>

masters-of-cats/image,containers/image,containers/image