Don't rely on SystemPrefix to set IOS_UNZIPPERED_TWIN_PREFIX_PATH

Mac Catalyst shouldn't have a SystemPrefix set in its SDK variant, so don't rely on that to set IOS_UNZIPPERED_TWIN_PREFIX_PATH, hard code it instead. Set MACOS_UNZIPPERED_TWIN_PREFIX_PATH too for completeness.

rdar://165798693

Author: ian-twilightcoder

Sources/SWBCore/Settings/BuiltinMacros.swift

@@ -120,6 +120,7 @@ public final class BuiltinMacros {
     public static let HOST_PLATFORM = BuiltinMacros.declareStringMacro("HOST_PLATFORM")
     public static let IOS_UNZIPPERED_TWIN_PREFIX_PATH = BuiltinMacros.declareStringMacro("IOS_UNZIPPERED_TWIN_PREFIX_PATH")
     public static let IPHONEOS_DEPLOYMENT_TARGET = BuiltinMacros.declareStringMacro("IPHONEOS_DEPLOYMENT_TARGET")
+    public static let MACOS_UNZIPPERED_TWIN_PREFIX_PATH = BuiltinMacros.declareStringMacro("MACOS_UNZIPPERED_TWIN_PREFIX_PATH")
     public static let MACOSX_DEPLOYMENT_TARGET = BuiltinMacros.declareStringMacro("MACOSX_DEPLOYMENT_TARGET")
     public static let NATIVE_ARCH = BuiltinMacros.declareStringMacro("NATIVE_ARCH")
     public static let NATIVE_ARCH_32_BIT = BuiltinMacros.declareStringMacro("NATIVE_ARCH_32_BIT")
@@ -1993,6 +1994,7 @@ public final class BuiltinMacros {
         MACOS_CREATOR_ARG,
         MACOS_TYPE,
         MACOS_TYPE_ARG,
+        MACOS_UNZIPPERED_TWIN_PREFIX_PATH,
         MAC_OS_X_PRODUCT_BUILD_VERSION,
         MAC_OS_X_VERSION_ACTUAL,
         MAC_OS_X_VERSION_MAJOR,

Sources/SWBCore/Settings/Settings.swift

@@ -2585,9 +2585,10 @@ private class SettingsBuilder: ProjectMatchLookup {
             sdkTable.pushContentsOf(defaultSettingsTable)
         }
 
-        // Set IOS_UNZIPPERED_TWIN_PREFIX_PATH to the Mac Catalyst variant's prefix path, even for the macOS variant.
-        if let macCatalystVariant = sdk.variant(for: MacCatalystInfo.sdkVariantName) {
-            sdkTable.push(BuiltinMacros.IOS_UNZIPPERED_TWIN_PREFIX_PATH, literal: macCatalystVariant.systemPrefix)
+        // Set twin prefix paths in macOS for Mac Catalyst.
+        if sdk.canonicalNameComponents?.basename == "macosx" {
+            sdkTable.push(BuiltinMacros.MACOS_UNZIPPERED_TWIN_PREFIX_PATH, literal: "")
+            sdkTable.push(BuiltinMacros.IOS_UNZIPPERED_TWIN_PREFIX_PATH, literal: "/System/iOSSupport")
         }
 
         // Add the settings provided by the SDK variant, if there is one.