Update emsdk_env.cmd to include the path to python and remove unnecessary backslashes. (#721)

When runtime uses all of the packs to reassemble emsdk, python needs to be in
a separate subdirectory. This change takes into account the new python location as
it was assumed in the root previously.

eng/emsdk_env.cmd

@@ -6,10 +6,19 @@ if "%EMSDK_PATH%"=="" (
   echo %EMSDK_PATH% is empty
   exit /b 1
 )
-set "TOADD_PATH_EMSCRIPTEN=%EMSDK_PATH%\emscripten"
+set "TOADD_PATH_EMSCRIPTEN=%EMSDK_PATH%emscripten"
 echo PATH += %TOADD_PATH_EMSCRIPTEN%
 set "PATH=%TOADD_PATH_EMSCRIPTEN%;%PATH%"
 
+REM python
+if "%EMSDK_PYTHON%"=="" (
+  echo %EMSDK_PYTHON% is empty
+  exit /b 1
+)
+set "TOADD_PATH_PYTHON=%EMSDK_PYTHON%"
+echo PATH += %TOADD_PATH_PYTHON%
+set "PATH=%TOADD_PATH_PYTHON%;%PATH%"
+
 REM llvm (clang, etc)
 if "%DOTNET_EMSCRIPTEN_LLVM_ROOT%"=="" (
   echo %DOTNET_EMSCRIPTEN_LLVM_ROOT% is empty
@@ -26,10 +35,10 @@ if "%DOTNET_EMSCRIPTEN_NODE_JS%"=="" (
   echo %DOTNET_EMSCRIPTEN_NODE_JS% is empty
   exit /b 1
 )
-set "TOADD_PATH_NODEJS=%~dpn0"
+set "TOADD_PATH_NODEJS=%DOTNET_EMSCRIPTEN_NODE_JS%"
 if not "%TOADD_PATH_EMSCRIPTEN%"=="%TOADD_PATH_NODEJS%" (
   if not "%TOADD_PATH_LLVM%"=="%TOADD_PATH_NODEJS%" (
-    echo PATH += %TOADD_PATH_NODEJS%
+    echo NODE PATH += %TOADD_PATH_NODEJS%
     set "PATH=%TOADD_PATH_NODEJS%;%PATH%"
   )
 )
@@ -39,7 +48,7 @@ if "%DOTNET_EMSCRIPTEN_BINARYEN_ROOT%"=="" (
   echo %DOTNET_EMSCRIPTEN_BINARYEN_ROOT% is empty
   exit /b 1
 )
-set "TOADD_PATH_BINARYEN=%DOTNET_EMSCRIPTEN_BINARYEN_ROOT%\bin"
+set "TOADD_PATH_BINARYEN=%DOTNET_EMSCRIPTEN_BINARYEN_ROOT%bin"
 if not "%TOADD_PATH_EMSCRIPTEN%"=="%TOADD_PATH_BINARYEN%" (
   if not "%TOADD_PATH_LLVM%"=="%TOADD_PATH_BINARYEN%" (
     if not "%TOADD_PATH_NODEJS%"=="%TOADD_PATH_BINARYEN%" (