Use of $(get_libdir) should be used to define proper lib installation location. Patch is attached.
Created attachment 258788 [details, diff] no-multilib installation patch
This is fixed in 5.2.10-r1. Thanks for the report and the patch. William
In 5.2.12-r1, I am removing this fix and setting --libexecdir=/lib/dhcpcd. Your patch would be correct if we were dealing with libdir, but that is not the case.