Logical inversion in diagnostic location for multiple 'default' labels in a switch statement

When multiple default labels are present in a single switch statement, Clang points the primary error diagnostic to the first occurrence. Logically, the first default label is perfectly valid; the program only becomes invalid when the second (duplicate) default label is encountered.
This creates a misleading debugging experience. In large, generated files, the developer is told that a valid line of code is an error, rather than being told that a later line is a duplicate of the first.

Minimal Reproducible Example：
```cpp
void f(int x) {
switch (x) {
default: break; // Line 3: Valid
case 1: break;
default: break; // Line 5: The actual duplicate/violation
}
}
```
Actual Behavior (Clang): Reports an error at Line 3.

Expected Behavior: The primary error should be at Line 5, with a supporting note pointing back to Line 3. This would align with how Clang handles other redefinition errors (e.g., duplicate function or variable definitions).