elf.h: syncronize DF_1_ flags with binutils

DF_1_STUB and DF_1_PIE were added in binutils-gdb commit
5c383f026242d25a3c21fdfda42e5ca218b346c8

include/elf.h

@@ -842,6 +842,8 @@ typedef struct {
 #define	DF_1_SYMINTPOSE	0x00800000
 #define	DF_1_GLOBAUDIT	0x01000000
 #define	DF_1_SINGLETON	0x02000000
+#define	DF_1_STUB	0x04000000
+#define	DF_1_PIE	0x08000000
 
 #define DTF_1_PARINIT	0x00000001
 #define DTF_1_CONFEXP	0x00000002