Add check for openSUSE when detecting bfd library

In ASTERISK-17842, some additional library checks were added to the configure
script so that the bfd library could be found on CentOS and Fedora systems.

As it turns out, openSUSE requires an additional library. This patch adds
another check to the configure script for openSUSE that will add that library.

Review: https://reviewboard.asterisk.org/r/2885/

(closes issue AST-1169)
Reported by: Guenther Kelleter
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Merged revisions 400073 from http://svn.asterisk.org/svn/asterisk/branches/1.8
........

Merged revisions 400075 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/12@400077 65c4cc65-6c06-0410-ace0-fbb531ad65f3

configure.ac

@@ -1215,6 +1215,11 @@ if test "${PBX_BFD}" = "0"; then
   AST_EXT_LIB_CHECK([BFD], [bfd], [bfd_check_format], [bfd.h], [-ldl -liberty])
 fi
 
+if test "${PBX_BFD}" = "0"; then
+  # openSUSE requires -lz
+  AST_EXT_LIB_CHECK([BFD], [bfd], [bfd_check_format], [bfd.h], [-ldl -liberty -lz])
+fi
+
 if test "x${OSARCH}" = "xlinux-gnu" ; then
   AST_EXT_LIB_CHECK([CAP], [cap], [cap_from_text], [sys/capability.h])
 fi