Convert all zero-argument functions to '(void)'

Otherwise, in C, it becomes a K&R function declaration which doesn't actually
type-check the number of arguments.

Change-Id: I0731a9fefca46fb1c266bfb1c33d464cf451a22e
Reviewed-on: https://boringssl-review.googlesource.com/1582
Reviewed-by: Adam Langley <agl@google.com>

include/openssl/engine.h

diff --git a/include/openssl/engine.h b/include/openssl/engine.h
index f2916b3..367e98e 100644
--- a/include/openssl/engine.h
+++ b/include/openssl/engine.h
@@ -37,7 +37,7 @@
 
 /* ENGINE_new returns an empty ENGINE that uses the default method for all
  * algorithms. */
-OPENSSL_EXPORT ENGINE *ENGINE_new();
+OPENSSL_EXPORT ENGINE *ENGINE_new(void);
 
 /* ENGINE_free decrements the reference counts for all methods linked from
  * |engine| and frees |engine| itself. */