Include mem.h for |CRYPTO_memcmp|

Change-Id: I3009326a5fa0c28bd3d214254e9beda4ea779833
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/40744
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: Adam Langley <agl@google.com>

crypto/fipsmodule/ec/felem.c

diff --git a/crypto/fipsmodule/ec/felem.c b/crypto/fipsmodule/ec/felem.c
index be178f5..e462514 100644
--- a/crypto/fipsmodule/ec/felem.c
+++ b/crypto/fipsmodule/ec/felem.c
@@ -14,6 +14,7 @@
 
 #include <openssl/ec.h>
 #include <openssl/err.h>
+#include <openssl/mem.h>
 
 #include <assert.h>