Cygwin: SetThreadName: avoid spurious debug message
The following debug message occassionally shows up in strace output:
SetThreadName: SetThreadDescription() failed.
00000000 10000000
The HRESULT of 0x10000000 is not an error, rather the set bit just
indicates that this HRESULT has been created from an NTSTATUS value.
Use the IS_ERROR() macro instead of just checking for S_OK.
Fixes:
d4689b99c686 ("Cygwin: Set threadnames with SetThreadDescription()")
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>