comments: fix misuses of "nor"

Signed-off-by: Justin Lebar <jlebar@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/http.h b/http.h
index cd37d58..a766066 100644
--- a/http.h
+++ b/http.h
@@ -13,8 +13,7 @@
 /*
  * We detect based on the cURL version if multi-transfer is
  * usable in this implementation and define this symbol accordingly.
- * This is not something Makefile should set nor users should pass
- * via CFLAGS.
+ * This shouldn't be set by the Makefile or by the user (e.g. via CFLAGS).
  */
 #undef USE_CURL_MULTI