[clang] [Clang] suggest headers on undeclared errors (#120388) (PR #140247)

[Vlad Serebrennikov via cfe-commits]

================
@@ -1489,6 +1490,7 @@ namespace cwg387 { // cwg387: 2.8
       a = gcd(a, b);
       b = gcd(3, 4);
       // expected-error at -1 {{use of undeclared identifier 'gcd'}}
+      // expected-note at -2 {{perhaps `#include <numeric>` is needed?}}
----------------
Endilll wrote:

```suggestion
      //   expected-note at -2 {{perhaps `#include <numeric>` is needed?}}
```

https://github.com/llvm/llvm-project/pull/140247