libcdecl: Parse function parameters in order.

libcdecl: Parse function parameters in order.

Currently the parser collects function parameters in reverse order,
then reverses them at the end.

There is no reason to do this.  It is only a slight restructuring of
the rules to collect parameters in the right order from the get go,
which means we can delete the duplicated list reversal code.

The grammar itself is also simpler this way, using two less nonterminals.