Update to v4.15 kernel headers.

Test: Compiles, boots bullhead/hikey960.
Change-Id: I118beb8b6cac0881b1270f9bf6981959297a41a8
diff --git a/libc/kernel/uapi/linux/stddef.h b/libc/kernel/uapi/linux/stddef.h
index a04729b..2a5fd95 100644
--- a/libc/kernel/uapi/linux/stddef.h
+++ b/libc/kernel/uapi/linux/stddef.h
@@ -16,7 +16,7 @@
  ***
  ****************************************************************************
  ****************************************************************************/
-#include <linux/compiler.h>
+#include <linux/compiler_types.h>
 #ifndef __always_inline
 #define __always_inline inline
 #endif