Merging r156047:

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r156047 | rjmccall | 2012-05-02 18:34:46 -0700 (Wed, 02 May 2012) | 4 lines

Merge x86-64-abi-sret-vs-2word-struct-param.cpp into the generic
x86_64-arguments.cpp test file and be sure to test the coerced
case as well.  Thanks to Wei-Ren Chen for bringing this test
to my attention.
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llvm-svn: 156673