Restore missing #include <stdint.h> to Android <sys/user.h>

This was lost in afa9c52715, but it turns out that it’s still
necessary.

Bug: google-breakpad:733
Change-Id: I4e0e4e4d2e80c22df1ff6b82e471905773c940a3
Reviewed-on: https://chromium-review.googlesource.com/675732
Reviewed-by: Joshua Peraza <jperaza@chromium.org>

src/common/android/include/sys/user.h

@@ -38,6 +38,10 @@
 // TODO(primiano): remove these changes after Chromium has stably rolled to
 // an NDK with the appropriate fixes. https://crbug.com/358831
 
+// With traditional headers, <sys/user.h> forgot to do this. Unified headers get
+// it right.
+#include <stdint.h>
+
 #include_next <sys/user.h>
 
 #include <android/api-level.h>