dhcpcd expects the directory /var/db/dhcpcd/ being present for the storage of various files. However, this directory is not created during a default build process of this package, causing error messages at run time. Suggesting to add a mkdir -p /var/db/dhcpcd/ in file /package/dhcpcd/dhcpcd.mk
This has been fixed in upstream dhcpcd since version 9.2.0 and https://github.com/rsmarples/dhcpcd/commit/4d695e1ca3b87b45d5e5fa5119ddcb8a086ca9a0
Fixed in git for 2020.11.x, thanks: https://git.buildroot.org/buildroot/commit/?h=2020.11.x&id=41cbb88372601346aedc2e9f7ab379ff481d1a2f