cleanup-misc.patch from patch #6230.

cleanup-misc.patch from patch #6230.

* acinclude.m4: Improve formatting.

* configure.ac: Ditto.  Don't check for headers whose presence is
never tested.  Don't use AC_C_CONST (we can assume that "const" is
implemented these days).  Don't pass default sizes to
AC_CHECK_SIZEOF, since modern Autoconf doesn't need them.  Don't
define FPREP_IEEE754, since it was not tested for.  Don't use
AC_FUNC_VPRINTF, since we never tested for it.

* float-format.h (enum float_format): Don't check for
FPREP_IEEE754 macro any longer.

* magic.h: Ditto.

* src/ui/debugger.c: Use debugger if HAVE_FORK is defined, not
HAVE_SYS_TYPES_H.  The latter is almost universal, but the former
is only available where it can be implemented.