With GCC 10, SOGoAptFormatter.m FTBS with the following error:
SOGoAptFormatter.m: In function ‘-[SOGoAptFormatter setPrivateTitleOnly]’:
SOGoAptFormatter.m:104:56: error: expected ‘)’ before ‘::’ token
104 | self->formatAction = @selector(titleOnlyForPrivateApt::);
Simply name the second argument, so gcc is happy.
Also add the `external` keyword to a header declared variable.
Fixes#5029
8507204e0d