Add missing include

Add missing sys/types.h include to fix building against musl libc.

Bug: 190084016
Test: m USE_HOST_HOST=true host-native
Change-Id: Ic75cb8db8978c3478cce65ec8838228bd245950d
diff --git a/brillo/streams/file_stream.h b/brillo/streams/file_stream.h
index bf54617..e2e29dd 100644
--- a/brillo/streams/file_stream.h
+++ b/brillo/streams/file_stream.h
@@ -5,6 +5,8 @@
 #ifndef LIBBRILLO_BRILLO_STREAMS_FILE_STREAM_H_
 #define LIBBRILLO_BRILLO_STREAMS_FILE_STREAM_H_
 
+#include <sys/types.h>
+
 #include <memory>
 
 #include <base/files/file_path.h>