lib/nolibc: Introduce strcat/bcopy/bzero functions

lib/nolibc: Introduce strcat/bcopy/bzero functions

The bcopy/bzero originate from BSD, but are often provided by libc on
other systems for compatibility. The strcat function is also added for
improved compatibility.

Signed-off-by: Marco Schlumpp <marco.schlumpp@gmail.com>
Reviewed-by: Razvan Deaconescu <razvand@unikraft.io>
Reviewed-by: Marc Rittinghaus <marc.rittinghaus@unikraft.io>
Approved-by: Marc Rittinghaus <marc.rittinghaus@unikraft.io>
Tested-by: Unikraft CI <monkey@unikraft.io>
GitHub-Closes: #627