makeqstrdata: Avoid encoding problems

Most users and the CI system are running in configurations where Python
configures stdout and stderr in UTF-8 mode.  However, Windows is different,
setting values like CP1252.  This led to a build failure on Windows, because
makeqstrdata printed Unicode strings to its stdout, expecting them to be
encoded as UTF-8.

This script is writing (stdout) to a compiler input file and potentially
printing messages (stderr) to a log or console.  Explicitly configure stdout to
use utf-8 to get consistent behavior on all platforms, and configure stderr so
that if any log/diagnostic messages are printed that cannot be displayed
correctly, they are still displayed instead of creating an error while trying
to print the diagnostic information.

I considered setting the encodings both to ascii, but this would just be
occasionally inconvenient to developers like me who want to show diagnostic
info on stderr and in comments while working with the compression code.

Closes: #3408

py/makeqstrdata.py

@@ -16,6 +16,9 @@ import collections
 import gettext
 import os.path
 
+sys.stdout.reconfigure(encoding='utf-8')
+sys.stderr.reconfigure(errors='backslashreplace')
+
 py = os.path.dirname(sys.argv[0])
 top = os.path.dirname(py)