AC_PROG_AWK fix for Solaris

[Stepan Kasal]

Hi,
  I suggest to apply the attached patch.
Problems with Solaris /bin/awk and /bin/nawk mishandling some simple
awk programs appear regularily on comp.lang.awk, and the answer is
always to use th POSIX awk in xpg4.

As always, I verified that make check passes.

Paul, OK to commit?

Have a nice day,
        Stepan Kasal

ac_prog_awk.patch
Description: Text document