ecpg: Output dir, source dir, stamp file argument for preproc/*.pl

ecpg: Output dir, source dir, stamp file argument for preproc/*.pl

This is in preparation for building postgres with meson / ninja.

When building with meson, commands are run at the root of the build tree. Add
an option to put build output into the appropriate place. This can be utilized
by src/tools/msvc/ for a minor simplification, which also provides some
coverage for the new option.

Add option to generate a timestamp for check_rules.pl, so that proper
dependencies on it having been run can be generated.

Reviewed-by: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Discussion: https://postgr.es/m/5e216522-ba3c-f0e6-7f97-5276d0270029@enterprisedb.com