Fixed source range for function template specializations.

template <class T> void foo();
template <> void foo<int>(); /* Spec 1 */
template <> void foo<int>(); /* Spec 2 */

If we look at the main location of the first explicit specialization (Spec 1) it can be seen that it points to the name of the *second* explicit specialization (Spec 2), which is a redeclaration of Spec1.
Hence, the source range obtained for Spec1 is not only inaccurate, but also invalid (the end location comes before the start location).

llvm-svn: 127002