[Build] Fix macos vs macosx issue.

The module triple bizarrely omits the "x" from "macosx".

Also disable some of this code on non-Apple platforms.

rdar://150944675

Author: al45tair

Runtimes/Core/cmake/modules/PlatformInfo.cmake

@@ -37,39 +37,46 @@ if(NOT SwiftCore_ARCH_SUBDIR)
   message(CONFIGURE_LOG "Swift Arch: ${arch}")
 endif()
 
-set(availability_platform_macosx "macOS")
-set(availability_platform_ios "iOS")
-set(availability_platform_watchos "watchOS")
-set(availability_platform_tvos "tvOS")
-set(availability_platform_xros "visionOS")
-set(availability_platform_bridgeos "bridgeOS")
+if(APPLE)
 
-if(NOT SwiftCore_SWIFT_AVAILABILITY_PLATFORM)
-  if(SwiftCore_MODULE_TRIPLE MATCHES ".*-([^-]+)-simulator$")
-    set(platform "${CMAKE_MATCH_1}")
-  elseif(SwiftCore_MODULE_TRIPLE MATCHES ".*-([^-]+)$")
-    set(platform "${CMAKE_MATCH_1}")
-  else()
-    message(FATAL_ERROR "Unable to extract platform name from triple ${SwiftCore_MODULE_TRIPLE}")
-  endif()
+  # Note: *moduleTriple* doesn't have an "x" on the end of "macos"; just to be
+  # safe, we support both cases here.
+  set(availability_platform_macos "macOS")
+  set(availaiblity_platform_macosx "macOS")
+  set(availability_platform_ios "iOS")
+  set(availability_platform_watchos "watchOS")
+  set(availability_platform_tvos "tvOS")
+  set(availability_platform_xros "visionOS")
+  set(availability_platform_bridgeos "bridgeOS")
 
-  if(availability_platform_${platform})
-    set(SwiftCore_SWIFT_AVAILABILITY_PLATFORM "${availability_platform_${platform}}")
-  else()
-    message(FATAL_ERROR "Unknown platform ${platform} for availability")
-  endif()
-endif()
+  if(NOT SwiftCore_SWIFT_AVAILABILITY_PLATFORM)
+    if(SwiftCore_MODULE_TRIPLE MATCHES ".*-([^-]+)-simulator$")
+      set(platform "${CMAKE_MATCH_1}")
+    elseif(SwiftCore_MODULE_TRIPLE MATCHES ".*-([^-]+)$")
+      set(platform "${CMAKE_MATCH_1}")
+    else()
+      message(FATAL_ERROR "Unable to extract platform name from triple ${SwiftCore_MODULE_TRIPLE}")
+    endif()
 
-if(SwiftCore_VARIANT_MODULE_TRIPLE)
-  if(SwiftCore_VARIANT_MODULE_TRIPLE MATCHES ".*-([^-]+)$")
-    set(platform "${CMAKE_MATCH_1}")
-  else()
-    message(FATAL_ERROR "Unable to extract platform name from triple ${SwiftCore_VARIANT_MODULE_TRIPLE}")
+    if(availability_platform_${platform})
+      set(SwiftCore_SWIFT_AVAILABILITY_PLATFORM "${availability_platform_${platform}}")
+    else()
+      message(FATAL_ERROR "Unknown platform ${platform} for availability")
+    endif()
   endif()
 
-  if(availability_platform_${platform})
-    set(SwiftCore_VARIANT_AVAILABILITY_PLATFORM "${availability_platform_${platform}}")
-  else()
-    message(FATAL_ERROR "Unknown platform ${platform} for variant availability")
+  if(SwiftCore_VARIANT_MODULE_TRIPLE)
+    if(SwiftCore_VARIANT_MODULE_TRIPLE MATCHES ".*-([^-]+)$")
+      set(platform "${CMAKE_MATCH_1}")
+    else()
+      message(FATAL_ERROR "Unable to extract platform name from triple ${SwiftCore_VARIANT_MODULE_TRIPLE}")
+    endif()
+
+    if(availability_platform_${platform})
+      set(SwiftCore_VARIANT_AVAILABILITY_PLATFORM "${availability_platform_${platform}}")
+    else()
+      message(FATAL_ERROR "Unknown platform ${platform} for variant availability")
+    endif()
   endif()
-endif()
+
+endif(APPLE)