* configure.in: Add configuration test for long double type existing
and set flag _HAVE_LONG_DOUBLE if true. Fix INIT_ARRAY (.init_array)
and _LDBL_EQ_DBL tests to not link so that will work with
cross-compilers.
* configure: Regenerated.
* Makefile.in: Ditto.
* newlib.hin: Add _HAVE_LONG_DOUBLE flag.
* libc/include/math.h: Change non-builtin defines for HUGE_VAL,
HUGE_VALF, and HUGE_VALL to be constant expressions. Add definitions
for the non-builtin case for INFINITY and NAN. Gate HUGE_VALL and
union __ldmath definitions with (new) _HAVE_LONG_DOUBLE.
*libm/common/s_infconst.c: Change definitions to use values from
float.h instead of non-so-portable integer forms. Mark as being
deprecated (because now removed from math.h, are not used anywhere
in Newlib, itself).
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