POSIX states:
The perror() function shall not change the orientation of the standard
error stream.

However, cygwin perror() function changes the orientation of stderr to
byte-oriented mode if stderr is not oriented yet.

Simple test case (chkperror.c) attached checks this behavior.

Expected result:
0
äöü: Invalid argument
0
äöü
1
äöü: Invalid argument

However, cygwin result:
0
äöü: Invalid argument
-1
▒▒▒
-1
äöü: Invalid argument

I have made a patch to solve this problem, attached. However, I am not
sure that calling _write_r() here is correct manner. I will appreciate
if anyone familiar with libc code comment or make suggestions.

-- 
Takashi Yano <takashi.yano@nifty.ne.jp>