[clang] [clang] Add the candiscard attribute to suppress nodiscard (PR #154943)

[Erich Keane via cfe-commits]

================
@@ -8,16 +8,26 @@
 using NI [[nodiscard]] = int; // expected-warning {{'[[nodiscard]]' attribute ignored when applied to a typedef}}
 using WURI [[clang::warn_unused_result]] = int;
 
+using EIgnored [[clang::candiscard]] = E;
+using NIIgnored [[clang::candiscard]] = NI;
+using WURIgnored [[clang::candiscard]] = WURI;
+
 @interface INTF
 - (int) a [[nodiscard]];
 + (int) b [[nodiscard]];
 - (expected<int>) c;
 + (expected<int>) d;
 - (E) e;
+- (EIgnored) e_ignored;
+- (E) e_ignored2 [[clang::candiscard]];
----------------
erichkeane wrote:

I THINK this is an ObjC method?  If so, then disregard the part I commented above regarding ObjC as a subjecdt, looks liek this was intentional/has reasonable semantics.

https://github.com/llvm/llvm-project/pull/154943