package/petitboot: add libxcrypt optional dependency
Fix the following build failure raised since bump of glibc to version
2.39 in commit b5680f53d60acf8ff6010082f873438a39bd5d97:
checking for crypt in -lcrypt... no
configure: error: in `/home/arbab/src/buildroot/output/build/petitboot-1.15':
configure: error: shadow/crypt libs required
Signed-off-by: Reza Arbab <arbab@linux.ibm.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>