Give ENGINE_free a return value.

This simplifies building against cryptography.io, which expects
ENGINE_free to return something.

Change-Id: Id1590abab7f47dae6b3a9d593fa7b0fe371c9912
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/35644
Reviewed-by: Adam Langley <agl@google.com>

crypto/engine/engine.c

diff --git a/crypto/engine/engine.c b/crypto/engine/engine.c
index 875f148..973a57c 100644
--- a/crypto/engine/engine.c
+++ b/crypto/engine/engine.c
@@ -41,9 +41,10 @@
   return engine;
 }
 
-void ENGINE_free(ENGINE *engine) {
+int ENGINE_free(ENGINE *engine) {
   // Methods are currently required to be static so are not unref'ed.
   OPENSSL_free(engine);
+  return 1;
 }
 
 // set_method takes a pointer to a method and its given size and sets

include/openssl/engine.h

diff --git a/include/openssl/engine.h b/include/openssl/engine.h
index 9d45952..ce60de4 100644
--- a/include/openssl/engine.h
+++ b/include/openssl/engine.h
@@ -40,8 +40,8 @@
 OPENSSL_EXPORT ENGINE *ENGINE_new(void);
 
 // ENGINE_free decrements the reference counts for all methods linked from
-// |engine| and frees |engine| itself.
-OPENSSL_EXPORT void ENGINE_free(ENGINE *engine);
+// |engine| and frees |engine| itself. It returns one.
+OPENSSL_EXPORT int ENGINE_free(ENGINE *engine);
 
 
 // Method accessors.