[2.079] Support minimal runtime

[kinke]

Thereby deferring requirements wrt. object.d declarations (Object, Throwable, TypeInfo, TypeInfo_Class, TypeInfo_Struct...) and paving the way for a minimal druntime.

This also greatly reduces the -vv output for tiny code samples, e.g., reduced test cases.

[dnadlinger]

I've been wanting to do this for quite some time, thanks – but wouldn't it be natural to ditch the runtime module altogether now?

[dnadlinger]

(I.e. create the functions directly in the requesting module.)

[kinke]

import core.stdc.stdio;
// pragma(LDC_no_moduleinfo);

void foo()
{
    printf("Hello LDC2 %d\n", (void*).sizeof);
}

-c -vv output of LDC 1.8: 376 lines
now: 123 lines
with pragma(LDC_no_moduleinfo): 64 lines

[kinke]

Wrt. runtime module, I wasn't sure whether it was just exploited as stringmap or whether caching the functions there brings some performance. Right now, the lazy 'declarers' may declare more than one function (same type, multiple names), so switching this exact scheme to forward-declaring directly into the desired module may yield a few superfluous declarations.

[dnadlinger]

Do we want to pass through the loc to all of these so we can generate error messages specifying the code that requires the feature in a minimal runtime setting? (Obviously a separate improvement.)

[kinke]

Yep, the loc would be nice to have of course. Given the elision of Module-/TypeInfos if there's no declaration, the chances of a missing TypeInfo should be pretty much restricted to a runtime function call requiring one of the few TypeInfo base types. As such, the existing loc param of getRuntimeFunction() should do fine, it'll just have to be forwarded to the LazyType error msg.

---

merge-2.079 green on Win64 now with this, on Linux too except for the 32-bit std.file unittests. :)

[kinke]

Well actually it'd probably be useful to do the runtime function lookup as early as possible. In various places, we first construct the args for the runtime function call (incl. TypeInfos) and afterwards do getRuntimeFunction() immediately before the call; the loc will be missed in these cases.

[kinke]

Expecting Win32 to succeed too now and so AppVeyor to become green.