Release 2.3.1 fails to build with GCC-11

[tillea]

Hi,
there was a bug reported against the Debian packaged version of mpqc version 2.3.1 (the latest tagged release I could find - see issue #59) I'd like to point you to a set of patches which are applied to the Debian package which is based on the SourceForge release and enabled us building the code up to the upgrade to GCC-11 which fails.
Kind regards, Andreas.