Add support for the OpenBSD for Bitrig.

Patch by David Hill.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@161344 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/configure b/configure
index 9c89a33..405567c 100755
--- a/configure
+++ b/configure
@@ -8947,7 +8947,7 @@
   shlibpath_overrides_runpath=yes
   ;;
 
-openbsd*)
+openbsd* | bitrig*)
   version_type=sunos
   sys_lib_dlsearch_path_spec="/usr/lib"
   need_lib_prefix=no