freebayes segmentation fault
Oh you silly sausage!
This obviously means that you are running out of stack memory. Apparently...

freebayes is creating a single string containing the entire vcf header, which gets quite big when the reference has a lot of contigs with long names, causing stack space depletion.

Try increasing the maximum stack size (in this example to 128M) and running your command again.
ulimit -S -s 131072