Definx HAVE_EVENT_BASE_LOOPEXITin msvc orconfig.h

Fixes bug 7308; bugfix on no released Tor, since we haven't actually built
right on MSVC in ages.

changes/msvc

+  o Build fixes (MSVC):
+    - Correctly define HAVE_EVENT_BASE_LOOPEXIT, since we only build
+      with MSVC when using Libevent 2.0 or later. Fixes bug 7308.
+      Reported by "ultramage".

src/win32/orconfig.h

@@ -247,4 +247,5 @@
 #define RSHIFT_DOES_SIGN_EXTEND
 #define FLEXIBLE_ARRAY_MEMBER 0
 #define HAVE_EVENT2_EVENT_H
+#define HAVE_EVENT_BASE_LOOPEXIT
 #define SHARE_DATADIR ""