awk: Update to version 20121220

awk: Update to version 20121220

* BK added  __attribute__((__noreturn__)) to a couple of lines in
  proto.h, to silence an enthusiastic checker.
* NK fixed obscure call by value bug in split(a[1],a) reported on
  9fans.  the management of temporary values is just a mess; he
  took a shortcut by making an extra string copy.
* tiny fiddle in setfval to eliminate -0 results in T.expr, which
  has irritated BK for 20+ years.

The README.DELETED file was relocated from the vendor branch to
the master branch to be consistent with how most of the vendor
branches are handled.