[CMake] Add support for building swift host libraries and tools on Android

Author: bulbazord

CMakeLists.txt

@@ -578,6 +578,8 @@ else()
     set(SWIFT_HOST_VARIANT_SDK_default "WINDOWS")
   elseif("${CMAKE_SYSTEM_NAME}" STREQUAL "Haiku")
     set(SWIFT_HOST_VARIANT_SDK_default "HAIKU")
+  elseif("${CMAKE_SYSTEM_NAME}" STREQUAL "Android")
+    set(SWIFT_HOST_VARIANT_SDK_default "ANDROID")
   elseif("${CMAKE_SYSTEM_NAME}" STREQUAL "Darwin")
     set(SWIFT_HOST_VARIANT_SDK_default "OSX")
   else()
@@ -702,6 +704,15 @@ elseif("${SWIFT_HOST_VARIANT_SDK}" STREQUAL "HAIKU")
   set(SWIFT_PRIMARY_VARIANT_SDK_default  "${SWIFT_HOST_VARIANT_SDK}")
   set(SWIFT_PRIMARY_VARIANT_ARCH_default "${SWIFT_HOST_VARIANT_ARCH}")
 
+elseif("${SWIFT_HOST_VARIANT_SDK}" STREQUAL "ANDROID")
+
+  set(SWIFT_HOST_VARIANT "android" CACHE STRING
+      "Deployment OS for Swift host tools (the compiler) [android].")
+
+  configure_sdk_unix("Android" "${SWIFT_HOST_VARIANT_ARCH}")
+  set(SWIFT_PRIMARY_VARIANT_SDK_default  "${SWIFT_HOST_VARIANT_SDK}")
+  set(SWIFT_PRIMARY_VARIANT_ARCH_default "${SWIFT_HOST_VARIANT_ARCH}")
+
 elseif("${SWIFT_HOST_VARIANT_SDK}" MATCHES "(OSX|IOS*|TVOS*|WATCHOS*)")
 
   set(SWIFT_HOST_VARIANT "macosx" CACHE STRING
@@ -746,7 +757,10 @@ endif()
 
 # Should we cross-compile the standard library for Android?
 is_sdk_requested(ANDROID swift_build_android)
-if(swift_build_android AND NOT "${SWIFT_ANDROID_NDK_PATH}" STREQUAL "")
+if(swift_build_android AND NOT "${SWIFT_HOST_VARIANT_SDK}" STREQUAL "ANDROID")
+  if ("${SWIFT_ANDROID_NDK_PATH}" STREQUAL "")
+    message(FATAL_ERROR "You must set SWIFT_ANDROID_NDK_PATH to cross-compile the Swift runtime for Android")
+  endif()
   if (NOT ("${CMAKE_HOST_SYSTEM_NAME}" STREQUAL "Darwin" OR "${CMAKE_HOST_SYSTEM_NAME}" STREQUAL "Linux"))
     message(FATAL_ERROR "A Darwin or Linux host is required to build the Swift runtime for Android")
   endif()