Apply asm redirections in syslog.h before first use [BZ #27087]

Similar to d0fa09a7, but for syslog.h when _FORTIFY_SOURCE > 0.
Fixes [BZ #27087] by applying long double-related asm redirections
before using functions in bits/syslog.h.

Tested with build-many-glibcs.py.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>