Eliminate the oddly-named Sema::ComparePropertiesInBaseAndSuper, which

Eliminate the oddly-named Sema::ComparePropertiesInBaseAndSuper, which
did a redundant traversal of the lexical declarations in the
superclass. Instead, when we declare a new property, look into the
superclass to see whether we're redeclaring the property. Goot for 1%
of -fsyntax-only time on Cocoa.h and a little less than 3% on my
modules test case.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@173073 91177308-0d34-0410-b5e6-96231b3b80d8