ldexp* tests: More tests.

ldexp* tests: More tests.

* tests/test-ldexp.h (test_function): Add some pseudo-randomized tests.
* tests/test-ldexp.c (RANDOM): New macro.
* tests/test-ldexpf.c (RANDOM): New macro.
* tests/test-ldexpl.c (RANDOM): New macro.
* modules/ldexp-tests (Files): Add tests/randomd.c.
(Makefile.am): Add randomd.c to test_ldexp_SOURCES.
* modules/ldexpf-tests (Files): Add tests/randomf.c.
(Makefile.am): Add randomf.c to test_ldexpf_SOURCES.
* modules/ldexpl-tests (Files): Add tests/randoml.c.
(Makefile.am): Add randoml.c to test_ldexpl_SOURCES.