error.c: "Unknown system error" should report errno value

[Martin Koeppe]

Hi all,

please consider printing the errno value together with "Unknown system 
error" if strerror() failed. It failed for me on Interix for 
errno=-1, which I'm interested to know about, just to get an idea what 
could be wrong, and that strerror() is not wrong.

Martin

error.diff
Description: Text document