ci: Build WasmKit on WebAssembly CI job

This activates executable tests in addition to IRGen tests.

Author: kateinoigakukun

utils/build-presets.ini

@@ -890,6 +890,7 @@ mixin-preset=
 mixin-preset=buildbot_linux
 
 llvm-targets-to-build=X86;ARM;AArch64;WebAssembly
+wasmkit
 build-wasm-stdlib
 # FIXME(katei): Test fails on a specific CI node.
 # https://github.com/apple/swift/issues/70980