Add IWYU export in nid.h file generated by objects.go

`IWYU pragma: export` was added to the openssl/base.h include in nid.h
in https://boringssl-review.googlesource.com/c/boringssl/+/77687 but
this file is generated by objects.go, so it ought to be added there
also.

Change-Id: I0ed894669778fde47f1b2fffba4c05c47a57261f
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/81067
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: David Benjamin <davidben@google.com>
Auto-Submit: Lily Chen <chlily@google.com>

crypto/obj/objects.go

@@ -407,7 +407,7 @@ func writeHeader(path string, objs *objects) error {
 #ifndef OPENSSL_HEADER_NID_H
 #define OPENSSL_HEADER_NID_H
 
-#include <openssl/base.h>
+#include <openssl/base.h>  // IWYU pragma: export
 
 #if defined(__cplusplus)
 extern "C" {

include/openssl/nid.h

@@ -17,7 +17,7 @@
 #ifndef OPENSSL_HEADER_NID_H
 #define OPENSSL_HEADER_NID_H
 
-#include <openssl/base.h>   // IWYU pragma: export
+#include <openssl/base.h>  // IWYU pragma: export
 
 #if defined(__cplusplus)
 extern "C" {