Replace with up-to-date version from official gpgme repository

[unprolix]

The previous version of this file in this repository was quite out of date and causing failure to detect gpgme on at least some modern systems. This version is directly from the official gpgme repository at https://git.gnupg.org/cgi-bin/gitweb.cgi?p=gpgme.git;a=blob_plain;f=src/gpgme.m4;hb=14b035034ab52c73f8d1aab2c475b3e8709600b4