gmtime and localtime aren't thread-safe so using them is unsound

[thestinger]

It's unclear if these wrappers in rust_builtin.c are actually used anywhere, but the code should be removed either way.

[alexcrichton]

This is only the case for mingw32.

[lifthrasiir]

cc #10480. We really want to decouple the datetime routines from the global states except when it is absolutely required (retrieving the current timezone, for example).

[deokjinkim]

As I know, gmtime and localtime are thread-safe on Windows(Microsoft) because such functions use static output area per thread.
And for other platform, gmtime_r and localtime_r are thread-safe version.
So I think current usage of above function is not problem.
Do you mean timezone variable(TZ) for localtime may cause thread-safety issue?

[klutzy]

The relevant code is rt/rust_builtin.c. libtime used them via rust_{gm,local}time but libtime has been moved out of tree.
cc #20861

[klutzy]

#21391 removed time wrappers. Fixed!