add NT_VMCOREDD to elf.h from linux v4.18

used for device driver dump in /proc/vmcore
new in linux commit 2724273e8fd00b512596a77ee063f49b25f36507

include/elf.h

@@ -685,6 +685,7 @@ typedef struct {
 #define NT_METAG_RPIPE	0x501
 #define NT_METAG_TLS	0x502
 #define NT_ARC_V2	0x600
+#define NT_VMCOREDD	0x700
 #define NT_VERSION	1