Revert r151638 because it causes assertion hit on PCH creation for Cocoa.h

Original log:
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Correctly track tags and enum members defined in the prototype of a function, and ensure they are properly scoped.

This fixes code such as:

enum e {x, y};
int f(enum {y, x} n) {
 return 0;
}

This finally fixes PR5464 and PR5477.
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I also reverted r151641 which was enhancement on top of r151638.

llvm-svn: 151667