CMake: Check platform availability on Apple

Platform availability is an Apple concept because Swift is shipped as
part of the OS. It doesn't make sense to check or to warn on other
platforms. Only checking and setting it for Apple platforms.

Author: etcwilde

Runtimes/Core/cmake/modules/PlatformInfo.cmake

@@ -43,47 +43,49 @@ if(NOT SwiftCore_ARCH_SUBDIR)
   message(CONFIGURE_LOG "Swift Arch: ${arch}")
 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(APPLE)
+  # 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(NOT SwiftCore_SWIFT_AVAILABILITY_PLATFORM)
-  if(SwiftCore_MODULE_TRIPLE MATCHES ".*-([^-]+)-simulator$")
-    set(platform "${CMAKE_MATCH_1}")
-  elseif(SwiftCore_MODULE_TRIPLE MATCHES ".*-([^-]+)-msvc$")
-    set(platform "${CMAKE_MATCH_1}")
-  elseif(SwiftCore_MODULE_TRIPLE MATCHES ".*-([^-]+)$")
-    set(platform "${CMAKE_MATCH_1}")
-  else()
-    message(WARNING "Unable to extract platform name from triple ${SwiftCore_MODULE_TRIPLE}")
-  endif()
+  if(NOT SwiftCore_SWIFT_AVAILABILITY_PLATFORM)
+    if(SwiftCore_MODULE_TRIPLE MATCHES ".*-([^-]+)-simulator$")
+      set(platform "${CMAKE_MATCH_1}")
+    elseif(SwiftCore_MODULE_TRIPLE MATCHES ".*-([^-]+)-msvc$")
+      set(platform "${CMAKE_MATCH_1}")
+    elseif(SwiftCore_MODULE_TRIPLE MATCHES ".*-([^-]+)$")
+      set(platform "${CMAKE_MATCH_1}")
+    else()
+      message(WARNING "Unable to extract platform name from triple ${SwiftCore_MODULE_TRIPLE}")
+    endif()
 
-  if(availability_platform_${platform})
-    set(SwiftCore_SWIFT_AVAILABILITY_PLATFORM "${availability_platform_${platform}}")
-  else()
-    set(SwiftCore_SWIFT_AVAILABILITY_PLATFORM "unknown")
-    message(WARNING "Unknown platform ${platform} for availability")
+    if(availability_platform_${platform})
+      set(SwiftCore_SWIFT_AVAILABILITY_PLATFORM "${availability_platform_${platform}}")
+    else()
+      set(SwiftCore_SWIFT_AVAILABILITY_PLATFORM "unknown")
+      message(WARNING "Unknown platform ${platform} for availability")
+    endif()
   endif()
-endif()
 
-set(SwiftCore_VARIANT_AVAILABILITY_PLATFORM "none")
-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 ${SwiftCore_VARIANT_MODULE_TRIPLE}")
-  endif()
+  set(SwiftCore_VARIANT_AVAILABILITY_PLATFORM "none")
+  if(SwiftCore_VARIANT_MODULE_TRIPLE)
+    if(SwiftCore_VARIANT_MODULE_TRIPLE MATCHES ".*-([^-]+)$")
+      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(WARNING "Unknown platform ${platform} for variant availability")
+    if(availability_platform_${platform})
+      set(SwiftCore_VARIANT_AVAILABILITY_PLATFORM "${availability_platform_${platform}}")
+    else()
+      message(WARNING "Unknown platform ${platform} for variant availability")
+    endif()
   endif()
 endif()