Remove stage0 allocator logic from MSVC in libstd

[alexcrichton]

We're updating the bootstrap compiler in #44154 which attempted to remove the MSVC-specific logic here (added in #43589) but I believe that caused this failure.

No time to debug just yet, but we should remove this one day!

[alexcrichton]

cc @aidanhs

[aidanhs]

Well beta-2017-08-29 does seem to have the code in it, so...hmm -

rust/src/librustc_trans/back/symbol_export.rs

Lines 87 to 93 in 1981099

	if tcx.sess.allocator_kind.get().is_some() {
	for method in ALLOCATOR_METHODS {
	local_crate.push((format!("__rust_{}", method.name),
	INVALID_DEF_ID,
	SymbolExportLevel::Rust));
	}
	}

[alexcrichton]

Oh I should also clarify that I'm not even sure this is the actual bug. I'm likely to close this after further investigation of updating the bootstrap compiler...

[alexcrichton]

Ok opening a new bug

[alexcrichton]

I opened up #44236, I think this may mean that __rust prefixes are the wrong ones and we're supposed to use the __rg ones, but there's no real motivation to fix this immediately so I'm not going to investigate further.