cgen: fix windows hot reload

[kbkpbot]

Fix issue #23214

Force generate _vinit_caller, _vcleanup_caller , these are needed under Windows, because dl.open() / dl.close() will call them when loading/unloading shared dll.

_{Huly®: V_0.6-21781}

[kbkpbot]

This PR will make -live work under Windows/TCC

D:\v\v\v\examples\hot_reload>v -live run message.v
OK reloads:    0 | Total reloads:    0 | Hello! Modify this message while the program is running.
OK reloads: 1869376609 | Total reloads: 544501614 | Hello! Modify this message while the program is running.
OK reloads: 1869376609 | Total reloads: 544501614 | Hello! Modify this message while the program is running.
OK reloads: 1869376609 | Total reloads: 544501614 | Hello! Modify this message while the program is running.
OK reloads: 1869376609 | Total reloads: 544501614 | Hello! Modify this message while the program is running.

But it seems that the reload counter has some problem.

[kbkpbot]

Maybe we can do this access the g_live_info symbol in main:

1. VV_EXPORTED_SYMBOL void* g_live_info = NULL;
2. In the shared dll, use GetProcessAddress get the g_live_info address.

[kbkpbot]

As under Windows, it is difficult that make the .dll access the caller's symbol, I suggest that move the g_live_info structure into the .dll.

As the .dll will be compiled and reloaded, it is not suitable put the g_live_info struct in the .dll.

[kbkpbot]

	if C.g_live_info == 0 {
		// When the current program is not compiled with -live, simply
		// return a new empty struct LiveReloadInfo in order to prevent
		// crashes. In this case, the background reloader thread is not
		// started, and the structure LiveReloadInfo will not get updated.
		// All its fields will be 0, but still safe to access.
		unsafe { C.g_live_info = int(&LiveReloadInfo{}) }
	}
	return unsafe { &LiveReloadInfo(C.g_live_info) }

This will generated a simplify code:

	if (g_live_info == 0) {
		{ // Unsafe block
			g_live_info =((int)(((v__live__LiveReloadInfo*)memdup(...}, sizeof(v__live__LiveReloadInfo)));
		}
	}
	return ((v__live__LiveReloadInfo*)(g_live_info));

[phcreery]

I see this overlaps most of everything from an old PR except https://github.com/vlang/v/pull/19621/files#diff-c8aafc93f5a132c1afb63f4c56a73731d8368f0076262fc9fe26a209661690b6

[spytheman]

There are some similarities, but this PR fixes a much deeper problem, and in a more maintainable way.