refactor: Include obj/build.h instead of build.h

Summary:
Partial backport of core PR11651 (commit 96b9281)
https://github.com/bitcoin/bitcoin/pull/11651/commits/96b92810a6a9719e03fe7004d5d5c2d6f7b7a5ff

Test Plan:

make check
ninja check

Reviewers: #bitcoin_abc, deadalnix, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D2970