Apply LIT(x) to floating point literals in libm-test.c

Apply LIT(x) to floating point literals in libm-test.c

With the exception of the second argument of nexttoward,
any suffixes should be stripped from the test input, and
the macro LIT(x) should be applied to use the correct
suffix for the type being tested.

This adds a new argument type "j" to gen-test-libm.pl
to signify an argument to a test input which does not
require fixup.  The test cases of nexttoward have
been updated to use this new feature.

This applies post-processing to all of the test inputs
through gen-libm-test.pl to strip literal suffixes and
apply the LIT(x) macro, with one exception stated above.
This seems a bit cleaner than tossing the macro onto
everything, albeit slightly more obfuscated.