Don't declare float / long double Bessel functions for XSI POSIX (bug 18977).
The float and long double versions of Bessel function (j0f, y1l, etc.)
are not in POSIX; only the double versions are. This patch
accordingly limits the declarations of those functions to __USE_MISC,
and fixes the conform/ test expectations which matched the previous
incorrect declarations.
Tested for x86_64 and x86 (testsuite, and that installed stripped
shared libraries are unchanged by this patch).