cd .. && /bin/sh /var/tmp/portage/sys-auth/pam_mount-2.15/work/pam_mount-2.15/build-aux/missing automake-1.13 --foreign src/Makefile /var/tmp/portage/sys-auth/pam_mount-2.15/work/pam_mount-2.15/build-aux/missing: line 81: automake-1.13: command not found WARNING: 'automake-1.13' is missing on your system. You should only need it if you modified 'Makefile.am' or 'configure.ac' or m4 files included by 'configure.ac'. [...] Reproducible: Always
Created attachment 393764 [details] build.log
sys-devel/automake-1.13.4:1.13 is not installed.
Your build log shows this: patching file src/Makefile.am Reversed (or previously applied) patch detected! Assuming -R. Hunk #1 succeeded at 8 with fuzz 2. That means there is some kind of patching (with a probably wrong patch) in your ebuild. However in the portage ebuild there is no patch afaics. Where is your pam_mount ebuild coming from? It's not the one from the portage tree.
You were right, the last version of pam_mount needed a patch (cryptsetup issue), which modified Makefile.am.