Make the default .mc file be `hostname`.mc if SENDMAIL_MC make.conf knob is not set.  This allows admins to create a per-machine configuration file while leaving the freebsd.mc template pristine.  Provide a rule to create `hostname`.mc from freebsd.mc if it doesn't exist.
Make the default .mc file be `hostname`.mc if SENDMAIL_MC make.conf knob
is not set.  This allows admins to create a per-machine configuration file
while leaving the freebsd.mc template pristine.  Provide a rule to create
`hostname`.mc from freebsd.mc if it doesn't exist.

PR:		misc/26299
MFC after:	8 days

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase