Assume C89 or later for math functions.

Assume C89 or later for math functions.

This simplifies the code, and makes it a bit smaller and faster,
and (most important) makes it easier to clean up signal handling
since we can stop worring about floating-point exceptions in
library code.  That was a problem before C89, but the problem
went away many years ago on all practical Emacs targets.
* configure.ac (frexp, fmod): Remove checks for these functions,
as we now assume them.
(FLOAT_CHECK_DOMAIN, HAVE_INVERSE_HYPERBOLIC, NO_MATHERR)
(HAVE_EXCEPTION):
Remove; no longer needed.
* admin/CPP-DEFINES (HAVE_FMOD, HAVE_FREXP, FLOAT_CHECK_DOMAIN)
(HAVE_INVERSE_HYPERBOLIC, NO_MATHERR): Remove.
* src/data.c, src/image.c, src/lread.c, src/print.c:
Don't include <math.h>; no longer needed.
* src/data.c, src/floatfns.c (IEEE_FLOATING_POINT): Don't worry that it
might be autoconfigured, as that never happens.
* src/data.c (fmod):
* src/doprnt.c (DBL_MAX_10_EXP):
* src/print.c (DBL_DIG):
Remove.  C89 or later always defines these.
* src/floatfns.c (HAVE_MATHERR, FLOAT_CHECK_ERRNO, FLOAT_CHECK_DOMAIN)
(in_float, float_error_arg, float_error_arg2, float_error_fn_name)
(arith_error, domain_error, domain_error2):
Remove all this pre-C89 cruft.  Do not include <errno.h> as that's
no longer needed -- we simply return what C returns.  All uses removed.
(IN_FLOAT, IN_FLOAT2): Remove.  All uses replaced with
the wrapped code.
(FLOAT_TO_INT, FLOAT_TO_INT2, range_error, range_error2):
Remove.  All uses expanded, as these macros are no longer used
more than once and are now more trouble than they're worth.
(Ftan): Use tan, not sin / cos.
(Flogb): Assume C89 frexp.
(fmod_float): Assume C89 fmod.
(matherr) [HAVE_MATHERR]: Remove; no longer needed.
(init_floatfns): Remove.  All uses removed.