[depends] boost: update to 1.70

Summary:
Backport of core PR15461.

This PR is known to cause 2 issues:

• The build (native) on ARM might be broken:

https://github.com/bitcoin/bitcoin/issues/17010

• The error messages are not helpful:

https://github.com/bitcoin/bitcoin/issues/16803

None of these issues are critical.

I kept (adapted) the patch to work around the first issue. It doesn't
provide a very solid guarantee but it can't hurt.

The second issue will be fixed in a future backport.

Note that due to boost cmake update, it is now required to set
Boost_USE_STATIC_RUNTIME to ON.

Test Plan:

make
make check

Run the Gitian builds.

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D5623