abuf: Allow use in host tools

Some header files included on the host are moving to use abuf, so adjust
the header-inclusion to bring in size_t correctly.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/abuf.h b/include/abuf.h
index 76e314b..de21cef 100644
--- a/include/abuf.h
+++ b/include/abuf.h
@@ -9,7 +9,11 @@
 #ifndef __ABUF_H
 #define __ABUF_H
 
+#ifdef USE_HOSTCC
+#include <sys/types.h>
+#else
 #include <linux/types.h>
+#endif
 
 /**
  * struct abuf - buffer that can be allocated and freed