git pushes for both 9.2.0 and trunk

[Gaius Mulley]

Hi,

I've pushed fixes for the gm2 on the gcc-9.2.0 branch
and also trunk branch.

In summary the gcc-9.2.0 branch changes include a string format
specifier bugfix (\n and \t) correctly translated when strings are
passed to external C functions.  Also mc has been backported from the
trunk and generates less gcc warnings.

In summary the trunk branch contains a portability fix to avoid a hard coded 
"nop"
and some smaller general bug fixes (potential uninitialised variables).
mc also generates less gcc warnings

regards,
Gaius