Eliminate xtime and its member sec, nsec

[frederick-vs-ja]

This PR is currently trying to replace uses of xtime with _timespec64, because _timespec64 is

• of a reserved name, and
• having the same member names as the standard timespec, and
• already available in all modes via <time.h>, and
• layout-compatible with xtime.

Definition of _timespec64 (not available in this repo):

struct _timespec64
{
    __time64_t tv_sec;
    long       tv_nsec;
};

Definition of xtime:

STL/stl/inc/xtimec.h

Lines 23 to 26 in 5e60382

	struct xtime { // store time with nanosecond resolution
	__time64_t sec;
	long nsec;
	};

Working towards #2206.

Every function in MSVC STL that has external linkage and involves xtime is either extern "C" or inline, so I think this PR doesn't break ABI.

I'm also trying to change the name of every function, except for constructor, involving xtime/_timespec64 in order to avoid polluting overload sets.

For constructor of unique_lock, I'm adding an explicit construction tag type - perhaps we can simply remove that ctor, and some other non-standard functions.

Edit: This PR is now removing non-standard overloads. One non-standard condition_variable::wait_until overload is changed to _Wait_until_sys_time and made private.

[StephanTLavavej]

Thanks! As I mentioned on Discord, I would indeed like to see all of the non-Standard functions be removed, limited only by anything that affects ABI. (Stuff that's separately compiled is generally clear because either the class is marked as exported, or the functions are marked, and there are explicit calling conventions so they look "weird". You can also double-check the export surface with dumpbin /exports and do a before-and-after comparison, if altering anything in stl/src that you're unsure about.)

[StephanTLavavej]

Thanks, I agree that this should preserve ABI. Leaving the parameter names as xt is fine, likewise for the filename xtime.cpp (too much of a headache to change for too little value).

[strega-nil-ms]

Thanks!

[StephanTLavavej]

I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed.

[StephanTLavavej]

Thanks for carefully removing this non-Standard machinery that was allowing calls like try_lock_until(nullptr) to compile! 🙀 🛠️ 😻