Fix the shared builders by exporting GCM symbols.

gcm_test.cc needs to access the internal GCM symbols. This is
unfortunate because it means that they have to be marked OPENSSL_EXPORT
just for this.

To compensate, modes.h is removed and its contents copied into
crypto/modes/internal.h.

Change-Id: I1777b2ef8afd154c43417137673a28598a7ec30e
Reviewed-on: https://boringssl-review.googlesource.com/6360
Reviewed-by: Adam Langley <alangley@gmail.com>
diff --git a/crypto/aes/mode_wrappers.c b/crypto/aes/mode_wrappers.c
index c706896..dc657dc 100644
--- a/crypto/aes/mode_wrappers.c
+++ b/crypto/aes/mode_wrappers.c
@@ -48,9 +48,9 @@
 
 #include <openssl/aes.h>
 
-#include "assert.h"
+#include <assert.h>
 
-#include <openssl/modes.h>
+#include "../modes/internal.h"
 
 
 void AES_ctr128_encrypt(const uint8_t *in, uint8_t *out, size_t len,