docs/WebAssembly.md: update Swift SDK build instructions

Swift SDKs require Swift SDK Generator to be built with its dependencies. Additionally, now that tests for Wasm stdlib run by default, we should include required tools. Embedded Swift build is also enabled in the documented invocation.

Author: MaxDesiatov

docs/WebAssembly.md

@@ -19,14 +19,18 @@ one wouldn't want end users to download multi-megabyte binaries.
 ## Building Swift SDK for WebAssembly
 
 The [Swift SDK](https://github.com/swiftlang/swift-evolution/blob/main/proposals/0387-cross-compilation-destinations.md)
-for WebAssembly is built using the following command:
+for WebAssembly is built and tested using the following command:
 
 ```bash
-./utils/build-script --build-wasm-stdlib
+./utils/build-script --build-wasm-stdlib --wasmkit --install-llvm --install-swift --swiftpm --install-swiftpm \
+  --libcxx --install-libcxx --llbuild --install-llbuild --swift-testing --install-swift-testing \
+  --swift-testing-macros --install-swift-testing-macros --build-embedded-stdlib --build-embedded-stdlib-cross-compiling \
+  '--llvm-install-components=llvm-ar;llvm-nm;llvm-ranlib;llvm-cov;llvm-profdata;llvm-objdump;llvm-objcopy;llvm-symbolizer;IndexStore;clang;clang-resource-headers;builtins;runtimes;clangd;libclang;dsymutil;LTO;clang-features-file;lld'
 ```
 
 This command will build the Swift compiler for the host platform and then build the Swift standard library
-for WebAssembly targets. The resulting Swift SDK `.artifactbundle` will be placed in the `../swift-sdk-generator/Bundles`
+for WebAssembly targets. Toolchain `lit.py` tests will run on the freshly built stdlib, both for embedded and non-embedded
+builds. The resulting Swift SDK `.artifactbundle` will be placed in the `../swift-sdk-generator/Bundles`
 directory.
 
 ## Building Swift SDK for WebAssembly without building the compiler