support/dependencies/dependencies.sh: require diagnostics perl package for mosh

Fixes:
http://autobuild.buildroot.net/results/820/820e98b1c126469b1f180f078d102ded43b9c40e/



scripts/Makefile.am of mosh-1.4.0 needs the perl diagnostics module on the host:

make[3]: Entering directory '/home/buildroot/autobuild/instance-2/output-1/build/mosh-1.4.0/scripts'
perl -Mdiagnostics -c ./mosh.pl
Can't locate diagnostics.pm in @INC (you may need to install the diagnostics module) (@INC contains: /home/buildroot/autobuild/instance-2/output-1/host/lib/perl /usr/local/lib64/perl5/5.36 /usr/local/share/perl5/5.36 /usr/lib64/perl5/vendor_perl /usr/share/perl5/vendor_perl /usr/lib64/perl5 /usr/share/perl5).
BEGIN failed--compilation aborted.

So add a check for it in dependencies.sh similar to the other perl modules.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
(cherry picked from commit 5be2d9bb)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>