morestack.S needs to be run through a preprocessor

[alexcrichton]

First off, this is super awesome! I'm quite excited to see where this goes.

When diagnosing rust-lang/cargo#1695 I tried to give this a spin, but I found that compiling libmorestack.a failed for me due to some preprocessor stuff. I think that llvm-mc doesn't have a built-in preprocessor (or it's at least quite limited), which is why we run it through gcc -E beforehand.

[japaric]

Does this error happen when cross-compiling to a specific arch? I haven't encountered this issue when cross compiling to mips, but I haven't tried other arches. I ask because I'd like to add a test for this, if possible.

(I'm aware that the Rust build system calls gcc -E in some places, but cross compiling to mips worked without them, so I didn't add them)

[alexcrichton]

Ah I was compiling for x86_64