elf.h: add PPC64_OPT_LOCALENTRY

allows calling extern functions without saving r2, for details see
glibc commit 0572433b5beb636de1a49ec6b4fdab830c38cdc5

include/elf.h

@@ -2241,6 +2241,7 @@ enum
 
 #define PPC64_OPT_TLS		1
 #define PPC64_OPT_MULTI_TOC	2
+#define PPC64_OPT_LOCALENTRY	4
 
 #define STO_PPC64_LOCAL_BIT	5
 #define STO_PPC64_LOCAL_MASK	0xe0