this actually isn't necessary here (#3)

it's not public api, so this prevents building on windows (and other
platforms that don't expose everything for linking), and we're building
the whole optree by hand at once, so there's no reason to use fixup
functions like this whose only use is for when we're building the optree
incrementally during parsing.
we shouldn't be shipping callparser1.h
add callparser_linkable to OBJECT in the Makefile.PL (#3)

i think this is the right thing, not quite sure