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

[Vlad Serebrennikov via cfe-commits]

================
@@ -26,14 +26,18 @@ void no_get_1() {
     auto [a0, a1] = A(); // expected-error {{decomposes into 3 elements}}
     auto [b0, b1] = B(); // expected-error {{decomposes into 3 elements}}
   }
-  auto [a0, a1, a2] = A(); // expected-error {{undeclared identifier 'get'}} expected-note {{in implicit initialization of binding declaration 'a0'}}
+  auto [a0, a1, a2] = A(); // expected-error {{undeclared identifier 'get'}} \
+                           // expected-note {{perhaps `#include <ranges>` is needed?}} \
----------------
Endilll wrote:

`<ranges>` is far from the only header that provides overloads of `std::get`, but probably the heaviest one for compile times. Also, this code is run in C++17 mode, and there's no `<ranges>` header in C++17. 

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