[PATCH] decodetree: Open files with encoding='utf-8'

["Philippe Mathieu-Daudé" <f4bug@amsat.org>]

When decodetree.py was added in commit 568ae7efae7, QEMU was
using Python 2 which happily reads UTF-8 files in text mode.
Python 3 requires either UTF-8 locale or an explicit encoding
passed to open(). Now that Python 3 is required, explicit
UTF-8 encoding for decodetree sources.

This fixes:

  $ /usr/bin/python3 scripts/decodetree.py test.decode
  Traceback (most recent call last):
    File "scripts/decodetree.py", line 1397, in <module>
      main()
    File "scripts/decodetree.py", line 1308, in main
      parse_file(f, toppat)
    File "scripts/decodetree.py", line 994, in parse_file
      for line in f:
    File "/usr/lib/python3.6/encodings/ascii.py", line 26, in decode
      return codecs.ascii_decode(input, self.errors)[0]
  UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 80:
  ordinal not in range(128)

Reported-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
---
 scripts/decodetree.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/scripts/decodetree.py b/scripts/decodetree.py
index 47aa9caf6d1..fa40903cff1 100644
--- a/scripts/decodetree.py
+++ b/scripts/decodetree.py
@@ -1304,7 +1304,7 @@ def main():
 
     for filename in args:
         input_file = filename
-        f = open(filename, 'r')
+        f = open(filename, 'r', encoding='utf-8')
         parse_file(f, toppat)
         f.close()
 
-- 
2.26.2