Fix for construct_env and list with tot build installed (#741)

emsdk.py

@@ -2182,6 +2182,17 @@ def load_releases_tags():
   if extra_release_tag:
     tags.append(extra_release_tag)
 
+  # Adds the currently installed SDK version, which might be a custom
+  # version.  This means it will show up in `list` and work with
+  # `construct_env`
+  version_file = sdk_path(os.path.join('upstream', '.emsdk_version'))
+  if os.path.exists(version_file):
+    with open(version_file) as f:
+      version = f.read()
+    version = version.split('-')[2]
+    if version not in tags:
+      tags.append(version)
+
   return tags, tags_fastcomp