fix missing dependency on .ll files (#1227)
fix missing dependency on .ll files (#1227)

Adds the .ll file as an input dependency to the custom flex rule.

Fixes #1224
p4lang/p4c,hanw/p4c,mbudiu-vmw/p4c-clone,p4lang/p4c,mbudiu-vmw/p4c-clone,p4lang/p4c,mbudiu-vmw/p4c-clone,hanw/p4c,p4lang/p4c,hanw/p4c,p4lang/p4c,hanw/p4c,mbudiu-vmw/p4c-clone