Activate INSTRUMENT_DOWNLOADS under clang analyzer as well as coverity

Patch from teor; ticket 13177.

src/or/or.h

@@ -14,7 +14,7 @@
 
 #include "orconfig.h"
 
-#ifdef __COVERITY__
+#if defined(__clang_analyzer__) || defined(__COVERITY__)
 /* If we're building for a static analysis, turn on all the off-by-default
  * features. */
 #ifndef INSTRUMENT_DOWNLOADS