The way this check mixes C and C++ started to cause issues since gpgme 1.18.0
But we can confidently skip the function check anyway.
--- a/configure.ac
+++ b/configure.ac
@@ -12302,4 +12302 @@
-        # progress_callback is the only func with plain C linkage
-        # checking for it also filters out older, KDE-dependent libgpgmepp versions
-        AC_CHECK_LIB(gpgmepp, progress_callback, [ GPGMEPP_LIBS=-lgpgmepp ],
-            [AC_MSG_ERROR(gpgmepp not found or not functional)], [])
+        GPGMEPP_LIBS=-lgpgmepp