Here's the diff on the source code. I can't explain how this diff would cause the function to disappear. Any suggestions?
$ diff musl-1.1.19/src/time/strftime.c /musl-1.1.22/src/time/strftime.c
9d8
< #include "libc.h"
12,13d10
< const char *__nl_langinfo_l(nl_item, locale_t);
<
48,50d44
< const char *__tm_to_tzname(const struct tm *);
< size_t __strftime_l(char *restrict, size_t, const char *restrict, const struct tm *restrict, locale_t);
<
184,186c178,179
< *l = snprintf(*s, sizeof *s, "%+.2d%.2d",
< (tm->__tm_gmtoff)/3600,
< abs(tm->__tm_gmtoff%3600)/60);
---
> *l = snprintf(*s, sizeof *s, "%+.4ld",
> tm->__tm_gmtoff/3600*100 + tm->__tm_gmtoff%3600/60);