build: make compress_json python3 compatible

This patch replaces a usage of `map` with list comprehension,
which makes the script Python 3 compatiable.

PR-URL: #25582
Reviewed-By: Refael Ackermann <refack@gmail.com>

tools/compress_json.py

@@ -24,7 +24,7 @@
 
   step = 20
   slices = (data[i:i+step] for i in xrange(0, len(data), step))
-  slices = map(lambda s: ','.join(str(ord(c)) for c in s), slices)
+  slices = [','.join(str(ord(c)) for c in s) for s in slices]
   text = ',\n'.join(slices)
 
   fp = open(sys.argv[2], 'w')