Adding compatibility versions for 5.6

5.6 corresponds with:
5.6: macOS 12.3, iOS 15.4, watchOS 8.5, tvOS 15.4

Author: etcwilde

lib/Basic/Platform.cpp

@@ -431,7 +431,9 @@ swift::getSwiftRuntimeCompatibilityVersionForTarget(
 
       return floorFor64(llvm::VersionTuple(5, 4));
     } else if (Major == 12) {
-      return floorFor64(llvm::VersionTuple(5, 5));
+      if (Minor <= 2)
+        return floorFor64(llvm::VersionTuple(5, 5));
+      return floorFor64(llvm::VersionTuple(5, 6));
     }
   } else if (Triple.isiOS()) { // includes tvOS
     llvm::VersionTuple OSVersion = Triple.getiOSVersion();
@@ -467,7 +469,9 @@ swift::getSwiftRuntimeCompatibilityVersionForTarget(
 
       return floorForArchitecture(llvm::VersionTuple(5, 4));
     } else if (Major <= 15) {
-      return floorForArchitecture(llvm::VersionTuple(5, 5));
+      if (Minor <= 3)
+        return floorForArchitecture(llvm::VersionTuple(5, 5));
+      return floorForArchitecture(llvm::VersionTuple(5, 6));
     }
   } else if (Triple.isWatchOS()) {
     llvm::VersionTuple OSVersion = Triple.getWatchOSVersion();
@@ -494,7 +498,9 @@ swift::getSwiftRuntimeCompatibilityVersionForTarget(
 
       return floorFor64bits(llvm::VersionTuple(5, 4));
     } else if (Major <= 8) {
-      return floorFor64bits(llvm::VersionTuple(5, 5));
+      if (Minor <= 4)
+        return floorFor64bits(llvm::VersionTuple(5, 5));
+      return floorFor64bits(llvm::VersionTuple(5, 6));
     }
   }