Update to v4.15 kernel headers.

Test: Compiles, boots bullhead/hikey960.
Change-Id: I118beb8b6cac0881b1270f9bf6981959297a41a8
diff --git a/libc/kernel/uapi/asm-generic/mman-common.h b/libc/kernel/uapi/asm-generic/mman-common.h
index a15624a..e752bb6 100644
--- a/libc/kernel/uapi/asm-generic/mman-common.h
+++ b/libc/kernel/uapi/asm-generic/mman-common.h
@@ -27,6 +27,7 @@
 #define PROT_GROWSUP 0x02000000
 #define MAP_SHARED 0x01
 #define MAP_PRIVATE 0x02
+#define MAP_SHARED_VALIDATE 0x03
 #define MAP_TYPE 0x0f
 #define MAP_FIXED 0x10
 #define MAP_ANONYMOUS 0x20