Build tzcode with hidden visibility.

Bug: 11156955
Change-Id: Ib98d837b56cbbdfd01687cb3054fe3103eec0da9
diff --git a/libc/tzcode/strftime.c b/libc/tzcode/strftime.c
index a926164..f996f48 100644
--- a/libc/tzcode/strftime.c
+++ b/libc/tzcode/strftime.c
@@ -144,7 +144,7 @@
 }
 
 size_t
-strftime_tz(s, maxsize, format, t, locale)
+__attribute__((visibility("default"))) strftime_tz(s, maxsize, format, t, locale)
 char * const        s;
 const size_t        maxsize;
 const char * const  format;