[utils] Fix update scripts output when run on python3.

This fixes a "bytes-like object is required, not 'str'" python3 error I hit on update_llc_test_checks.py (but present on the other scripts as well) by matching what update_mca_test_checks.py already does, plus I've added an explicit 'utf-8' encoding.

llvm-svn: 352633
diff --git a/llvm/utils/update_analyze_test_checks.py b/llvm/utils/update_analyze_test_checks.py
index 64e64e0..4d1d912 100755
--- a/llvm/utils/update_analyze_test_checks.py
+++ b/llvm/utils/update_analyze_test_checks.py
@@ -186,7 +186,7 @@
       print('Writing %d lines to %s...' % (len(output_lines), test), file=sys.stderr)
 
     with open(test, 'wb') as f:
-      f.writelines([l + '\n' for l in output_lines])
+      f.writelines(['{}\n'.format(l).encode('utf-8') for l in output_lines])
 
 
 if __name__ == '__main__':