Support symbol versioning

Bug: http://b/20139821
Change-Id: I64122a0fb0960c20b2ce614161b7ab048456b681
diff --git a/libc/include/elf.h b/libc/include/elf.h
index 801d9ff..df768ba 100644
--- a/libc/include/elf.h
+++ b/libc/include/elf.h
@@ -194,4 +194,10 @@
 
 #define NT_GNU_BUILD_ID 3
 
+#define VER_FLG_BASE 0x1
+#define VER_FLG_WEAK 0x2
+
+#define VER_NDX_LOCAL  0
+#define VER_NDX_GLOBAL 1
+
 #endif /* _ELF_H */