If EAGAIN == EWOULDBLOCK, only need to check errno for one of them

If EAGAIN == EWOULDBLOCK, only need to check errno for one of them

Solaris <sys/errno.h> has:
 #define EWOULDBLOCK       EAGAIN
so checking (errno == EAGAIN || errno == EWOULDBLOCK) is overkill.

This leads cppcheck 1.62 to complain:
[xserver/os/io.c:365] -> [xserver/os/io.c:365]: (style) Same expression on both sides of '||'.
[xserver/os/io.c:941] -> [xserver/os/io.c:941]: (style) Same expression on both sides of '||'.

This quiets it, and reduces the number of calls Solaris Studio cc
generates to the __errno() function to get the thread-specific errno value.

Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Signed-off-by: Keith Packard <keithp@keithp.com>