build.info: Make it possible to use compiled programs as generators

build.info: Make it possible to use compiled programs as generators

Our goal is to be able to produce fipsmodule.cnf with the help of
'openssl fipsinstall', using the openssl program that we build.

This refactors the generatesrc code in all the build file templates to
replace $generator and $generator_incs with $gen0, $gen_args and $gen_incs,
which makes it easier and more consistent to manipulate different bits
of the generator command, and also keeps the variable names consistent
while not overly long.

Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/14320)