[ops2c] ops2c is already quiet and doesn't need --quiet
[ops2c] various fixes for symbol visibility and constants translation
[ops2c] clean up/fix write barrier generation

The generated core_ops.c now doesn't seem to contain any subtantial
differences from what's in git and all non-opsc tests pass with the
exception t/library/yaml_tiny.t.
[ops2c] bring back the makefile rules for ops2c's generated files