bytevectors: Fix IEEE-754 endianness conversion.
Fixes <http://bugs.gnu.org/11310>.
Reported by Klaus Stehle <klaus.stehle@uni-tuebingen.de>.
* libguile/ieee-754.h: Remove.
* libguile/Makefile.am (noinst_HEADERS): Remove `ieee-754.h'.
* libguile/bytevectors.c (scm_ieee754_float, scm_ieee754_double): New
unions.
(float_to_foreign_endianness, float_from_foreign_endianness,
double_to_foreign_endianness, double_from_foreign_endianness): Rewrite
in terms of the new unions.
* test-suite/tests/bytevectors.test ("2.8 Operations on IEEE-754
Representations")["single, little endian", "single, big endian",
"double, little endian", "double, big endian"]: New tests.