math: add LDBL_CLASSIFY_COMPAT support

math: add LDBL_CLASSIFY_COMPAT support

If a platform does not define "long-double-fcts = yes" in its
Makefiles and it does define __NO_LONG_DOUBLE_MATH in its installed
headers, it will currently create exported symbols for __finitel,
__isinfl, and __isnanl that can't be reached from userspace by
correct use of the finite(), isinf(), or isnan() macros in <math.h>.

To avoid this situation, by default for such platforms we now no
longer export these symbols, thus causing appropriate link-time
errors.  However, for platforms that previously exported these
symbols, we continue to do so as compat symbols; this is enabled
by adding LDBL_CLASSIFY_COMPAT to math_private.h for the platform.

For tile, remove the now-unnecessary exports of those functions from
libc and libm.