[ADT] Deprecate variadic StringSwitch::CasesLower. NFC. (llvm#166016)

Suggest the initializer_list overload instead. I plan to deprecate the
last variadic `.Cases` in a separate PR.

For more context, see llvm#163117.

Author: kuhar

clang/lib/CIR/CodeGen/CIRGenOpenACCClause.cpp

@@ -126,7 +126,7 @@ class OpenACCClauseCIREmitter final
         .CaseLower("default", mlir::acc::DeviceType::Default)
         .CaseLower("host", mlir::acc::DeviceType::Host)
         .CaseLower("multicore", mlir::acc::DeviceType::Multicore)
-        .CasesLower("nvidia", "acc_device_nvidia",
+        .CasesLower({"nvidia", "acc_device_nvidia"},
                     mlir::acc::DeviceType::Nvidia)
         .CaseLower("radeon", mlir::acc::DeviceType::Radeon);
   }

llvm/include/llvm/ADT/StringSwitch.h

@@ -173,6 +173,7 @@ class StringSwitch {
     return CasesLowerImpl(CaseStrings, Value);
   }
 
+  [[deprecated("Pass cases in std::initializer_list instead")]]
   StringSwitch &CasesLower(StringLiteral S0, StringLiteral S1, T Value) {
     return CasesLowerImpl({S0, S1}, Value);
   }

llvm/lib/MC/MCParser/MasmParser.cpp

@@ -5323,10 +5323,10 @@ void MasmParser::initializeDirectiveKindMap() {
 bool MasmParser::isMacroLikeDirective() {
   if (getLexer().is(AsmToken::Identifier)) {
     bool IsMacroLike = StringSwitch<bool>(getTok().getIdentifier())
-                           .CasesLower("repeat", "rept", true)
+                           .CasesLower({"repeat", "rept"}, true)
                            .CaseLower("while", true)
-                           .CasesLower("for", "irp", true)
-                           .CasesLower("forc", "irpc", true)
+                           .CasesLower({"for", "irp"}, true)
+                           .CasesLower({"forc", "irpc"}, true)
                            .Default(false);
     if (IsMacroLike)
       return true;