Add pywin32 to windows python installation (#487)

Fixes: #458

emsdk_manifest.json

@@ -324,6 +324,26 @@
     "activated_cfg": "PYTHON='%installation_dir%/python.exe'",
     "activated_env": "EMSDK_PYTHON=%installation_dir%/python.exe"
   },
+  {
+    "id": "python",
+    "version": "3.7.4-pywin32",
+    "bitness": 32,
+    "arch": "x86",
+    "windows_url": "python-3.7.4-embed-win32+pywin32.zip",
+    "activated_path": "%installation_dir%",
+    "activated_cfg": "PYTHON='%installation_dir%/python.exe'",
+    "activated_env": "EMSDK_PYTHON=%installation_dir%/python.exe"
+  },
+  {
+    "id": "python",
+    "version": "3.7.4-pywin32",
+    "bitness": 64,
+    "arch": "x86_64",
+    "windows_url": "python-3.7.4-embed-amd64+pywin32.zip",
+    "activated_path": "%installation_dir%",
+    "activated_cfg": "PYTHON='%installation_dir%/python.exe'",
+    "activated_env": "EMSDK_PYTHON=%installation_dir%/python.exe"
+  },
   {
     "id": "java",
     "version": "8.152",
@@ -702,7 +722,7 @@
   {
     "version": "releases-upstream-%releases-tag%",
     "bitness": 64,
-    "uses": ["node-12.9.1-64bit", "python-3.7.4-64bit", "java-8.152-64bit", "releases-upstream-%releases-tag%-64bit"],
+    "uses": ["node-12.9.1-64bit", "python-3.7.4-pywin32-64bit", "java-8.152-64bit", "releases-upstream-%releases-tag%-64bit"],
     "os": "win",
     "custom_install_script": "emscripten_npm_install"
   },
@@ -723,7 +743,7 @@
   {
     "version": "releases-fastcomp-%releases-tag%",
     "bitness": 64,
-    "uses": ["node-12.9.1-64bit", "python-3.7.4-64bit", "java-8.152-64bit", "releases-fastcomp-%releases-tag%-64bit"],
+    "uses": ["node-12.9.1-64bit", "python-3.7.4-pywin32-64bit", "java-8.152-64bit", "releases-fastcomp-%releases-tag%-64bit"],
     "os": "win",
     "custom_install_script": "emscripten_npm_install"
   },