$NetBSD$

Detect and link with libbacktrace (if linking is needed).

--- src/CMakeLists.txt.orig	2015-08-03 10:14:45.000000000 +0000
+++ src/CMakeLists.txt
@@ -112,10 +112,12 @@ if (NVT_TIMEOUT)
   add_definitions (-DNVT_TIMEOUT=${NVT_TIMEOUT})
 endif (NVT_TIMEOUT)
 
+find_package(Backtrace)
+
 target_link_libraries (openvassd ${LIBOPENVAS_NASL_LDFLAGS}
                        ${LIBOPENVAS_BASE_LDFLAGS} ${LIBOPENVAS_MISC_LDFLAGS}
                        ${LIBOPENVAS_OMP_LDFLAGS} ${GLIB_LDFLAGS}
-                       ${GCRYPT_LDFLAGS})
+                       ${GCRYPT_LDFLAGS} ${Backtrace_LIBRARY})
 
 ## Tests