This target doesn't build, due to a missing gas/config/te-obsd.h file.
It's been that way since the commit switching to elf, in 2002.
https://lists.gnu.org/archive/html/bug-gnu-utils/2002-07/msg00128.html
* configure.tgt (alpha-*-openbsd*): Use em=nbsd.
+2016-06-24 Alan Modra <amodra@gmail.com>
+
+ * configure.tgt (alpha-*-openbsd*): Use em=nbsd.
+
2016-06-23 Maciej W. Rozycki <macro@imgtec.com>
* config/tc-mips.c (b_reloc_p): New function.
alpha-*-osf*) fmt=ecoff ;;
alpha-*-linux*ecoff*) fmt=ecoff ;;
alpha-*-linux-*) fmt=elf em=linux ;;
- alpha-*-netbsd*) fmt=elf em=nbsd ;;
- alpha-*-openbsd*) fmt=elf em=obsd ;;
+ alpha-*-netbsd* | alpha-*-openbsd*) fmt=elf em=nbsd ;;
arc-*-elf*) fmt=elf ;;
arc*-*-linux*) fmt=elf bfd_gas=yes ;;