xl: Fix CHK_ERRNO()

xl: Fix CHK_ERRNO()

The macro CHK_ERRNO() was being used to check two different error schemes, and
succeeded at neither.

Split the macro into two; CHK_SYSCALL() for calls which return -1 and set
errno on error, and CHK_ERRNOVAL() for calls which return an errno.

In both cases, ensure that strerror() now gets called with the error integer.

Coverity ID: 1055570 1090374 1130516

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
CC: Ian Campbell <Ian.Campbell@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Release-acked-by: George Dunlap <george.dunlap@eu.citrix.com>