Exclude msys from path fix function. (#1078)

Fixes: #911

emsdk.py

@@ -527,7 +527,7 @@ def untargz(source_filename, dest_dir):
 # See https://msdn.microsoft.com/en-us/library/aa365247.aspx#maxpath and http://stackoverflow.com/questions/3555527/python-win32-filename-length-workaround
 # In that mode, forward slashes cannot be used as delimiters.
 def fix_potentially_long_windows_pathname(pathname):
-  if not WINDOWS:
+  if not WINDOWS or MSYS:
     return pathname
   # Test if emsdk calls fix_potentially_long_windows_pathname() with long
   # relative paths (which is problematic)