If Dovecot update/build with custombuild fails with an error:
sha1.h:80: error: static or type qualifiers in abstract declarator
here is a guide on how to fix it (for advanced users or sysadmins).
To get it fixed and upgrade/install dovecot with custombuild run the following command
until you get the message to retry the build (because it failed).
*** The make has failed, would you like to try to make again? (y,n):
Don't enter either y or n but press ctrl+z to push the build to the background and run this code:
Then get the build process back to the foreground with:perl -pi -e 's/define STATIC_ARRAY static/define STATIC_ARRAY/' dovecot-2.2.25/config.h
The process is still waiting for you to enter 'y' or 'n', although you don't see that. Type 'y' and press enter. The build will 'make' dovecot again without extracting the tar.gz and will succeed.