ARROW-7013: [C++] arrow-dataset pkgconfig is incomplete
ARROW-7013: [C++] arrow-dataset pkgconfig is incomplete

I've verified that this now does the right thing working on R bindings on https://github.com/apache/arrow/pull/5454.

Closes #5747 from nealrichardson/arrow-dataset-pkgconfig and squashes the following commits:

023d56a15 <Neal Richardson> Feedback from @kou
3d1da976a <Neal Richardson> Add missing config for arrow-dataset pkgconfig

Authored-by: Neal Richardson <beb59f0141269d2d04e73d0dcc1967b64ba87e13@gmail.com>
Signed-off-by: Sutou Kouhei <73218711cdd5d5c30ac66da3cc4d9d9204caf34b@clear-code.com>

apache/arrow,laurentgo/arrow,icexelloss/arrow,apache/arrow,kou/arrow,wesm/arrow,apache/arrow,kou/arrow,xhochy/arrow,laurentgo/arrow,laurentgo/arrow,icexelloss/arrow,xhochy/arrow,cpcloud/arrow,xhochy/arrow,apache/arrow,wesm/arrow,laurentgo/arrow,cpcloud/arrow,xhochy/arrow,cpcloud/arrow,xhochy/arrow,laurentgo/arrow,cpcloud/arrow,cpcloud/arrow,wesm/arrow,wesm/arrow,laurentgo/arrow,laurentgo/arrow,laurentgo/arrow,wesm/arrow,laurentgo/arrow,xhochy/arrow,apache/arrow,kou/arrow,cpcloud/arrow,kou/arrow,kou/arrow,icexelloss/arrow,apache/arrow,kou/arrow,kou/arrow,icexelloss/arrow,cpcloud/arrow,wesm/arrow,icexelloss/arrow,icexelloss/arrow,kou/arrow,laurentgo/arrow,apache/arrow,laurentgo/arrow,xhochy/arrow,cpcloud/arrow,apache/arrow,icexelloss/arrow,laurentgo/arrow,xhochy/arrow,icexelloss/arrow,cpcloud/arrow,kou/arrow,cpcloud/arrow,xhochy/arrow,icexelloss/arrow,apache/arrow,wesm/arrow,apache/arrow,xhochy/arrow,cpcloud/arrow,icexelloss/arrow,xhochy/arrow,xhochy/arrow,cpcloud/arrow,kou/arrow,cpcloud/arrow,laurentgo/arrow,laurentgo/arrow,wesm/arrow,wesm/arrow,kou/arrow,icexelloss/arrow,apache/arrow,wesm/arrow,xhochy/arrow,wesm/arrow,laurentgo/arrow,kou/arrow,kou/arrow,icexelloss/arrow,apache/arrow,apache/arrow,icexelloss/arrow,cpcloud/arrow,xhochy/arrow,apache/arrow,kou/arrow,wesm/arrow,xhochy/arrow,wesm/arrow,wesm/arrow,icexelloss/arrow