Run autoupdate and clean up autoconf usage

Run autoupdate and clean up autoconf usage

We can assume that the return type of a signal handler is void.
We can assume that, if sys/time.h exists, it can be included
with time.h.

* bootstrap: Get the latest version
* configure.ac: Require a newer version of autoconf.
Remove unnecessary AC_PROG_CC_C99 (already have AC_PROC_CC).
Remove unnecessary AC_AIX, AC_ISC_POSIX, AC_MINIX.
Remove unnecessary AC_HEADER_STDC, AC_HEADER_TIME, AC_TYPE_SIGNAL.
Use strerror to search for the cposix library.
* src/commands.c (fatal_error_signal): Assume return type is void.
* src/commands.h: Ditto.
* src/job.c: Ditto.
* src/job.h: Ditto.
* src/main.c: Ditto.
* src/makeint.h: Ditto.
Don't bother with TIME_WITH_SYS_TIME.
* src/remote-cstms.c: Check HAVE_SYS_TIME_H.
* src/config.ami.template: Remove RETSIGTYPE.
* src/config.h-vms.template: Ditto.
* src/config.h.W32.template: Ditto.
Remove TIME_WITH_SYS_TIME.