Signed-off-by: falkTX <falktx@falktx.com>

- Migrate pkg-config checks from atleast_version.
- Check ppoll with a fragment, since the function_name argument has been
  removed.

This is the last version on the 1.8.x branch. The build system will be
updated to the 1.9.x branch in a later commit.

This reverts commit cf3f8205c4.

It was a good initiative, but waf 2.0 introces backward incompatible
changes that break the pkg-config checks. The config checks will be
updated before migrating to waf 2.0.