One pass.

One pass.

Second pass was used because some information (which influences
early parts of the generated code, e.g enum with condition names
or YYMAXFILL definition) becomes available only at the end of first
pass.

I isolate all (I hope so) these things and generate stubs for them,
which are filled later. I restructured output as follows: the whole
output consists of source and header, each of them is a list of
blocks (corresponding to re2c blocks in source file), each block
is a list of code fragments (which can be either regular strings
with code or stubs that will be filled later).