Define write_profiling functions only in profile library [BZ #31756]

libc.so doesn't use nor export write_profiling functions.  There is no
point to define them in libc.so nor in libc.a.  Fix BZ #31756 by defining
them only in profile library.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>