TOOLS/file2string.py: support outputting to file

Another modification for the upcoming meson build. Meson can capture the
stdout and redirect it to a file. However, this is considered a hack.
It's better to just add a few lines to this script and write a file
directly.

TOOLS/file2string.py

@@ -39,5 +39,10 @@ def file2string(infilename, infile, outfile):
         outfile.write('"' + ''.join(conv[c] for c in line) + '"\n')
 
 if __name__ == "__main__":
+    if len(sys.argv) < 2:
+        outfile = sys.stdout
+    else:
+        outfile = open(sys.argv[2], "w")
+
     with open(sys.argv[1], 'rb') as infile:
-        file2string(sys.argv[1], infile, sys.stdout)
+        file2string(sys.argv[1], infile, outfile)