Do IWYU to fix building with gcc.

This is likely due to https://pdfium-review.googlesource.com/69071
reducing the numbers of headers being included.

Change-Id: Ia838f2f5ebda7a75f96a1e2541c4f0ed801ec9ec
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/69136
Commit-Queue: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
diff --git a/fpdfsdk/fpdf_attachment.cpp b/fpdfsdk/fpdf_attachment.cpp
index 529f3e6..7c47fb6 100644
--- a/fpdfsdk/fpdf_attachment.cpp
+++ b/fpdfsdk/fpdf_attachment.cpp
@@ -4,6 +4,8 @@
 
 #include "public/fpdf_attachment.h"
 
+#include <limits.h>
+
 #include <memory>
 #include <utility>