Fix i686 struct returning in some scenarios#5726

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brson wants to merge 2 commits intorust-lang:incomingfrom

brson:struct-return

Commits on Apr 15, 2013

rt: Move test functions to rust_test_helpers.cpp
brson
committed

Commits on Apr 17, 2013

rustc: Use an out pointer to return structs in x86 C ABI. #5347
brson
committed