This reverts commit ce9e0fc9.

This reverts commit 276dfc61.

Need this to correctly determine sysroot in rustc

Revert "stdlib: Migrate rust_file_is_dir() over to the C stack, and add a void type" due to build bustage on Windows

This reverts commit 9698ef89.

rustc: Allow calling native functions on the C stack that take generic arguments. They get turned into i8 pointers.

This reverts commit 6e56ec00.

This reverts commit 6e652588.

This reverts commit 007ec666.

Issue #667

It wasn't safe (computing the rval might invalidate the lval addr), and needlessly
complicating things (code was already building up intermediary results to work
around other unsafeties).

Issue #667

Issue #667

The retptr passed to a function will now often be the actual
destination of the returned value (as in `{field1: func1()}`).

This splits mk/stageN.mk into host.mk and target.mk and makes
the build rules somewhat simpler - there's no more building from stageN
into stageN+1; instead we always build from stageN(host) to
stageN(target) then promote from stageN(target) to stageN+1(host).

Add a big honkin explaination right at the top of Makefile.in

We'll copy the files to the right location. Still need to rpath.

Issue #529

rustc: Stub a --stack-growth option; it's behind a flag for now because it requires patches to LLVM.