Update to v4.15 kernel headers.

Test: Compiles, boots bullhead/hikey960.
Change-Id: I118beb8b6cac0881b1270f9bf6981959297a41a8
diff --git a/libc/kernel/uapi/linux/elf.h b/libc/kernel/uapi/linux/elf.h
index 8aa1011..bf35f6c 100644
--- a/libc/kernel/uapi/linux/elf.h
+++ b/libc/kernel/uapi/linux/elf.h
@@ -347,11 +347,13 @@
 #define NT_S390_VXRS_HIGH 0x30a
 #define NT_S390_GS_CB 0x30b
 #define NT_S390_GS_BC 0x30c
+#define NT_S390_RI_CB 0x30d
 #define NT_ARM_VFP 0x400
 #define NT_ARM_TLS 0x401
 #define NT_ARM_HW_BREAK 0x402
 #define NT_ARM_HW_WATCH 0x403
 #define NT_ARM_SYSTEM_CALL 0x404
+#define NT_ARM_SVE 0x405
 #define NT_METAG_CBUF 0x500
 #define NT_METAG_RPIPE 0x501
 #define NT_METAG_TLS 0x502