build: Remove -I for everything but project root

Summary:
Remove -I from build system for everything but the project root,
and built-in dependencies.

Partial backport of core PR11651 (commit 0c71521)
https://github.com/bitcoin/bitcoin/pull/11651/commits/0c715214dd2d03b66a366a87bf6d2c576c0176c2

Completes T649

Test Plan:

make check
ninja check
ninja bitcoin-bench

Reviewers: #bitcoin_abc, deadalnix, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D3016