The CPAN Testers Matrix shows Digest::SHA1 version 2.13 (the latest) passing tests all the way back to 5.8.4. However, if you look at the report for a 5.8.4 "PASS" you will see that the toolchain of the smoke tester includes ExtUtils::MakeMaker version 6.56, which is as recent as December 2009 (much newer than Perl 5.8.4).

It would be a simple fix for the author to add a CONFIGURE_REQUIRES directive in Makefile.PL. When he builds the distribution META.yml and META.json will be written with that dependency, and when your cpan installer stumbles across it, the newer version of EU::MM will be installed before Makefile.PL is ever run, which should solve the problem. If you sent in a brief patch to Makefile.PL for Digest::SHA1, via Digest::SHA1's RT page, I bet the maintainer would add it to the next release, whenever that is.

Meanwhile, try updating EU::MM and attempting a new installation.