unistd fortify macros broken

[Nitin Gupta]

When adding -D_FORTIFY_SOURCE=2, the uclibc unistd.h file includes
bits/unistd.h, which apparently doesn't exist.

The problem code in unistd.h is here:
/* Define some macros helping to catch buffer overflows.  */
#if __USE_FORTIFY_LEVEL > 0 && !defined __cplusplus
# include <bits/unistd.h>
#endif

One suggestion is there should be a warning in its place if the macros don't actually
do anything.