build: build with gssapi if detected

Reviewed-by: Andreas Schneider <asn@cryptomilk.org>

src/CMakeLists.txt

@@ -64,6 +64,13 @@ if (WITH_ZLIB)
   )
 endif (WITH_ZLIB)
 
+if (GSSAPI_LIBS)
+  set(LIBSSH_LINK_LIBRARIES
+    ${LIBSSH_LINK_LIBRARIES}
+    ${GSSAPI_LIBS}
+  )
+endif (GSSAPI_LIBS)
+
 set(LIBSSH_LINK_LIBRARIES
   ${LIBSSH_LINK_LIBRARIES}
   CACHE INTERNAL "libssh link libraries"