Issue title: Unoptimized code too big for 32-bit linker
 Issue body: So the `auto-mac-32-nopt` build slave failed trying to link librustc.dylib. The error being `LLVM ERROR: Section too large, can't encode r_address (0x10007fc) into 24 bits of scattered relocation entry.` which I interpret as being too big for the linker to handle.

 Comments: 
 Comment 0: cc @graydon 

I think we'll have to disable the 32-bit no-opt bots for now.

 Comment 1: Maybe this will be resolved after a snapshot.

 Comment 2: Seems resolved to me; auto-mac-32-nopt seems to be enabled.

 Comment 3: @catamorphism: I don't think the 64-bit one is enabled but not 32-nopt: http://buildbot.rust-lang.org/builders

 Comment 4: Both of the Mac 32-nopt builders seem to be enabled now:

http://buildbot.rust-lang.org/builders/auto-mac-32-nopt-c

http://buildbot.rust-lang.org/builders/auto-mac-32-nopt-t

Closing.

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