HBSD: Revert "REALLOCARRAY: remove m4 reallocarray implementation temporaly."

This reverts commit de63c75d406190264505ad238a33446e28899b7a.
HBSD USERLAND: try a better compile error fix after reallocarray import

github-issue: #70
Signed-off-by: Oliver Pinter <oliver.pntr@gmail.com>
CC: David Carlier <david.carlier@hardenedbsd.org>