Log Message:
Build fix on OpenBSD, borrowed from OpenBSD ports.

Quote from the commit log(ports/editors/emacs21/Makefile version 1.10).
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Work around the fact that emacs undump knows too much about the layout
of elf files (or thinks it does). These assumptions were just broken
by binutils/ld changes to put GOT and PLT into their own PT_LOAD sections.
Thus BSS is no longer part of the DATA PT_LOAD section. This is a
workaround using the '-Z' compatibility flag which disables the GOT/PLT
padding.