cmake: If we don't have gssapi libs, disable it.

ConfigureChecks.cmake

@@ -201,6 +201,10 @@ if (WITH_DEBUG_CALLTRACE)
   set(DEBUG_CALLTRACE 1)
 endif (WITH_DEBUG_CALLTRACE)
 
+if (WITH_GSSAPI AND NOT GSSAPI_LIBS)
+    set(WITH_GSSAPI 0)
+endif (WITH_GSSAPI AND NOT GSSAPI_LIBS)
+
 # ENDIAN
 if (NOT WIN32)
     test_big_endian(WORDS_BIGENDIAN)