[SemaCXX] Param diagnostic matches overload logic
Summary:
Given the following test program:
```
class C {
public:
int A(int a, int& b);
};
int C::A(const int a, int b) {
return a * b;
}
```
Clang would produce an error message that correctly diagnosed the
redeclaration of `C::A` to not match the original declaration (the
parameters to the two declarations do not match -- the original takes an
`int &` as its 2nd parameter, but the redeclaration takes an `int`). However,
it also produced a note diagnostic that inaccurately pointed to the
first parameter, claiming that `const int` in the redeclaration did not
match the unqualified `int` in the original. The diagnostic is
misleading because it has nothing to do with why the program does not
compile.
The logic for checking for a function overload, in
`Sema::FunctionParamTypesAreEqual`, discards cv-qualifiers before
checking whether the types are equal. Do the same when producing the
overload diagnostic.
Reviewers: rsmith
Reviewed By: rsmith
Subscribers: cpplearner, cfe-commits
Tags: #clang
Differential Revision: https://reviews.llvm.org/D57032
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@352831
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