Remove build.mk usage

First step when creating the `configure` script is currently using
make. This is helpful when developing buildsystem to only rebuild
`configure` and `main/php_config.h.in` files when one of the *.m4
or configure.ac file changes and saves the developer time a little.

Realistically however, it is not needed that much considering the
times of several seconds to fully rebuild the configure script and
configuration header. The next step when running the `configure`
script is much more time consuming so performance on buildconf
level is a bit questionable and won't be noticed on today's
systems.

Additionally:
- buildconf now removes cache and all targets and uses -f option on
  the first step i.e. autoconf. The autoheader does not need the -f
  option in this case.

Closes GH-4437

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