only set D_WASI_EMULATED_PTHREAD when required

Author: yowl

eng/native/gen-buildsys.cmd

@@ -65,7 +65,10 @@ if /i "%__Arch%" == "wasm" (
         set "WASI_SDK_PATH=!WASI_SDK_PATH:\=/!"
         if not "!WASI_SDK_PATH:~-1!" == "/" set "WASI_SDK_PATH=!WASI_SDK_PATH!/"
         set __CmakeGenerator=Ninja
-        set __ExtraCmakeParams=%__ExtraCmakeParams% -DCLR_CMAKE_TARGET_OS=wasi -DCLR_CMAKE_TARGET_ARCH=wasm "-DWASI_SDK_PREFIX=!WASI_SDK_PATH!" "-DCMAKE_TOOLCHAIN_FILE=!WASI_SDK_PATH!/share/cmake/wasi-sdk-p2.cmake" "-DCMAKE_SYSROOT=!WASI_SDK_PATH!share/wasi-sysroot" "-DCMAKE_CROSSCOMPILING_EMULATOR=node --experimental-wasm-bigint --experimental-wasi-unstable-preview1 -D_WASI_EMULATED_PTHREAD"
+        set __ExtraCmakeParams=%__ExtraCmakeParams% -DCLR_CMAKE_TARGET_OS=wasi -DCLR_CMAKE_TARGET_ARCH=wasm "-DWASI_SDK_PREFIX=!WASI_SDK_PATH!" "-DCMAKE_TOOLCHAIN_FILE=!WASI_SDK_PATH!/share/cmake/wasi-sdk-p2.cmake" "-DCMAKE_SYSROOT=!WASI_SDK_PATH!share/wasi-sysroot" "-DCMAKE_CROSSCOMPILING_EMULATOR=node --experimental-wasm-bigint --experimental-wasi-unstable-preview1"
+        if not "!__CMakeArgs:multithread=!" == "!__CMakeArgs!" (
+            set __ExtraCmakeParams=%__ExtraCmakeParams% -D_WASI_EMULATED_PTHREAD"
+        )
     )
 ) else (
     set __ExtraCmakeParams=%__ExtraCmakeParams%  "-DCMAKE_SYSTEM_VERSION=10.0"