Don't do the fortify_source checks if we can determine, at
compile time, that the provided operation is safe.
This avoids silliness like calling fortify source on things like:
size_t len = strlen("asdf");
printf("%d\n", len);
and allows the compiler to optimize this code to:
printf("%d\n", 4);
Defer to gcc's builtin functions instead of pointing our code
to the libc implementation.
Change-Id: I5e1dcb61946461c4afaaaa983e39f07c7a0df0ae
a44e9afdd1