Fix IWYU issue in internal header

For some reason, Bazel previously wasn't compiling our headers
standalone and now is. Doing so is now tripping a whole series of bugs
and deficiencies in Bazel that I'm still trying to figure out, but this
issue is at least legitimate.

Bug: 362664827
Change-Id: I3ca953a14ac36fa283fefcb42ff7805993247785
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/70647
Auto-Submit: David Benjamin <davidben@google.com>
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: Adam Langley <agl@google.com>

crypto/fipsmodule/aes/internal.h

diff --git a/crypto/fipsmodule/aes/internal.h b/crypto/fipsmodule/aes/internal.h
index 7d2db3b..a89da46 100644
--- a/crypto/fipsmodule/aes/internal.h
+++ b/crypto/fipsmodule/aes/internal.h
@@ -17,6 +17,8 @@
 
 #include <stdlib.h>
 
+#include <openssl/aes.h>
+
 #include "../../internal.h"
 
 #if defined(__cplusplus)