[analyzer] Follow up to r167762 - precisely determine the adjustment

conditions.

The adjustment is needed only in case of dynamic dispatch performed by
the analyzer - when the runtime declaration is different from the static
one.

Document this explicitly in the code (by adding a helper). Also, use
canonical Decls to avoid matching against the case where the definition
is different from found declaration.

This fix suppresses the testcase I added in r167762, so add another
testcase to make sure we do test commit r167762.

llvm-svn: 167780