guard *_chk() related stuff with UCLIBC_HAS_FORTIFY

guard *_chk() related stuff with UCLIBC_HAS_FORTIFY

Guard x86_64 memset_chk/memcpy_chk be guarded by UCLIBC_HAS_FORTIFY.
Compile ssp.c if one of SSP/FORTIFY is defined.
Guard __chk_fail() with UCLIBC_HAS_FORTIFY and move its prototype to libc-internal.h.
Disable _FORTIFY_SOURCE if UCLIBC_HAS_FORTIFY is not set.

The config option itself is omitted on purpose,
headers need to be reviewed and generic *_chk() functions need to be first provided.

Signed-off-by: Peter S. Mazinger <ps.m@gmx.net>