[Build] Fix availability platform macros.

These need to be defined always; we'll set them to "unknown" and "none"
respectively if they end up being something we don't understand.

rdar://150966361

Author: al45tair

Runtimes/Core/cmake/modules/PlatformInfo.cmake

@@ -37,46 +37,46 @@ if(NOT SwiftCore_ARCH_SUBDIR)
   message(CONFIGURE_LOG "Swift Arch: ${arch}")
 endif()
 
-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")
 
-  # 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 ".*-([^-]+)$")
-      set(platform "${CMAKE_MATCH_1}")
-    else()
-      message(FATAL_ERROR "Unable to extract platform name from triple ${SwiftCore_MODULE_TRIPLE}")
-    endif()
-
-    if(availability_platform_${platform})
-      set(SwiftCore_SWIFT_AVAILABILITY_PLATFORM "${availability_platform_${platform}}")
-    else()
-      message(FATAL_ERROR "Unknown platform ${platform} for availability")
-    endif()
+set(SwiftCore_SWIFT_AVAILABILITY_PLATFORM "unknown")
+if(NOT SwiftCore_SWIFT_AVAILABILITY_PLATFORM)
+  if(SwiftCore_MODULE_TRIPLE MATCHES ".*-([^-]+)-simulator$")
+    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(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_SWIFT_AVAILABILITY_PLATFORM "${availability_platform_${platform}}")
+  else()
+    message(WARNING "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 ${platform} for variant availability")
-    endif()
+set(SwiftCore_VARIANT_AVAILABILITY_PLATFORM "none")
+if(SwiftCore_VARIANT_MODULE_TRIPLE)
+  if(SwiftCore_VARIANT_MODULE_TRIPLE MATCHES ".*-([^-]+)$")
+    set(platform "${CMAKE_MATCH_1}")
+  else()
+    message(FATAL_ERROR "Unable to extract platform name from triple ${SwiftCore_VARIANT_MODULE_TRIPLE}")
   endif()
 
-endif(APPLE)
+  if(availability_platform_${platform})
+    set(SwiftCore_VARIANT_AVAILABILITY_PLATFORM "${availability_platform_${platform}}")
+  else()
+    message(WARNING "Unknown platform ${platform} for variant availability")
+  endif()
+endif()