Add an ERRNO_CHECK() preprocessor macro

Add an ERRNO_CHECK() preprocessor macro

In a number of situations in pthreads-related code, a common sequence of
steps is taken: if the value returned by a library function is not 0,
pass errno to strerror_r(), log the string returned by the latter, and
immediately abort execution.  Add an ERRNO_CHECK() preprocessor macro
which takes those exact steps and use it wherever (conveniently)
possible.

Notes:

 1. The "log the return value of strerror_r() and abort" pattern is used
    in a number of other places that this commit does not touch; only
    "!= 0" checks followed by isc_error_fatal() calls with
    non-customized error messages are replaced here.

 2. This change temporarily breaks file name & line number reporting for
    isc__mutex_init() errors, to prevent breaking the build.  This issue
    will be rectified in a subsequent change.