Merging r143751:

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r143751 | chandlerc | 2011-11-04 16:49:01 -0700 (Fri, 04 Nov 2011) | 3 lines

Switch the C++ include interface in the ToolChain to use the same naming
as the system include interface before I start adding implementations of
it to individual ToolChain implementations.
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llvm-svn: 143929