[wasm][build] Recognize wasi-wasm32 as valid host

wasi-wasm32 support in build system was added in
b1236e9 but we forgot to add it to the
host for the case when we are building the standalone stdlib for the
target.

Author: kateinoigakukun

CMakeLists.txt

@@ -1043,6 +1043,14 @@ elseif("${SWIFT_HOST_VARIANT_SDK}" STREQUAL "ANDROID")
   set(SWIFT_PRIMARY_VARIANT_SDK_default  "${SWIFT_HOST_VARIANT_SDK}")
   set(SWIFT_PRIMARY_VARIANT_ARCH_default "${SWIFT_HOST_VARIANT_ARCH}")
 
+elseif("${SWIFT_HOST_VARIANT_SDK}" STREQUAL "WASI")
+  set(SWIFT_HOST_VARIANT "wasi" CACHE STRING
+      "Deployment OS for Swift host tools (the compiler) [wasi]")
+
+  configure_sdk_unix("WASI" "wasm32")
+  set(SWIFT_PRIMARY_VARIANT_SDK_default  "${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

utils/build-script-impl

@@ -481,6 +481,7 @@ function verify_host_is_supported() {
       | watchsimulator-arm64    \
       | watchos-armv7k          \
       | watchos-arm64_32        \
+      | wasi-wasm32             \
       | android-armv7           \
       | android-aarch64         \
       | android-x86_64)