[liftoff] Use C++14 constexpr switch

Since C++14, we can use a switch in a constexpr function.

R=ahaas@chromium.org

Bug: v8:9686, v8:9687
Change-Id: I082a7be6c54d6c705b678f19aa56bdb7a3313f80
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1786284Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63596}

src/wasm/baseline/liftoff-register.h

@@ -32,15 +32,18 @@ static inline constexpr bool needs_reg_pair(ValueType type) {
   return kNeedI64RegPair && type == kWasmI64;
 }
 
-// TODO(clemensh): Use a switch once we require C++14 support.
 static inline constexpr RegClass reg_class_for(ValueType type) {
-  return needs_reg_pair(type)  // i64 on 32 bit
-             ? kGpRegPair
-             : type == kWasmI32 || type == kWasmI64  // int types
-                   ? kGpReg
-                   : type == kWasmF32 || type == kWasmF64  // float types
-                         ? kFpReg
-                         : kNoReg;  // other (unsupported) types
+  switch (type) {
+    case kWasmF32:
+    case kWasmF64:
+      return kFpReg;
+    case kWasmI32:
+      return kGpReg;
+    case kWasmI64:
+      return kNeedI64RegPair ? kGpRegPair : kGpReg;
+    default:
+      return kNoReg;  // unsupported type
+  }
 }
 
 // Maximum code of a gp cache register.