illumos gate

Build error:

    ../../../common/mdb/mdb_fmt.c: In function 'mdb_fmt_print':
    ../../../common/mdb/mdb_fmt.c:779:8: error: 'buf' may be used uninitialized in this function [-Werror=maybe-uninitialized]
        if (mdb_tgt_aread(t, as, buf, fp->f_size, addr) !=
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    cc1: all warnings being treated as errors
    *** Error code 1
    dmake: Fatal error: Command failed for target `mdb_fmt.o'
    Current working directory /code/illumos-gate/usr/src/cmd/mdb/intel/ia32/mdb

However, this error is there because our die() and fail() functions do not return, but gcc does not know about it.

While there, nuke CNOWARN_UNINIT.