Fix build regression with DO_XSI_MATH disabled
Fix build regression with DO_XSI_MATH disabled

Commit ea38f4d89 (math: add exception handling functionality) adds a
regression so that build configurations that have DO_C99_MATH enabled
and DO_XSI_MATH disabled will not link. This commit moves the files with
the bessel functions from DO_C99_MATH to DO_XSI_MATH. It looks like they
are not even contained in C99.

Signed-off-by: Ronald Wahl <18bb69c7479970b0c0b6e387cbe7353a09282081@raritan.com>

wbx-github/uclibc-ng,wbx-github/uclibc-ng,kraj/uclibc-ng,wbx-github/uclibc-ng,kraj/uclibc-ng,wbx-github/uclibc-ng,kraj/uclibc-ng,kraj/uclibc-ng