Merging r196712:

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r196712 | rafael | 2013-12-07 17:13:22 -0800 (Sat, 07 Dec 2013) | 12 lines

Fix pr18174.

Clang outputs LLVM one top level decl at a time. This combined with the
visibility computation code looking for the newest NamespaceDecl would cause
it to produce different results for nested namespaces.

The two options for producing consistent results are
* Delay codegen of anything inside a namespace until the end of the file.
* Don't look for the newest NamespaceDecl.

This patch implements the second option.
This matches the gcc behavior too.
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llvm-svn: 196745