Port to AIX 7.2 ksh93

Problem reported in <https://savannah.gnu.org/support/?111102>.
* lib/autotest/general.m4:
* lib/m4sugar/m4sh.m4 (_AS_REEXEC_WITH_SHELL):
* tests/wrapper.as:
Port to AIX 7.2 ksh93, whidh mishandles ${1+"$@"}, by not using
that construct.
7 files changed