[StdlibUnittest] add a TestRunPredicate for WASI

Author: glessard

Diff for: stdlib/private/StdlibUnittest/StdlibUnittest.swift

@@ -2444,6 +2444,8 @@ public enum TestRunPredicate : CustomStringConvertible {
 
   case haikuAny(reason: String)
 
+  case wasiAny(reason: String)
+
   case objCRuntime(/*reason:*/ String)
   case nativeRuntime(/*reason:*/ String)
 
@@ -2565,6 +2567,9 @@ public enum TestRunPredicate : CustomStringConvertible {
     case .haikuAny(reason: let reason):
       return "haikuAny(*, reason: \(reason))"
 
+    case .wasiAny(reason: let reason):
+      return "wasiAny(*, reason: \(reason))"
+
     case .objCRuntime(let reason):
       return "Objective-C runtime, reason: \(reason))"
     case .nativeRuntime(let reason):
@@ -2947,6 +2952,14 @@ public enum TestRunPredicate : CustomStringConvertible {
         return false
       }
 
+    case .wasiAny:
+      switch _getRunningOSVersion() {
+      case .wasi:
+        return true
+      default:
+        return false
+      }
+
     case .objCRuntime:
 #if _runtime(_ObjC)
       return true