Allow to extend and override the sanitizers options

Summary:
This cause the values from the user environment to be appended to the
options, allowing for adding options or overriding some. Update the CI
to use this feature.

Depends on D5689.

Test Plan: Run the build-asan, build-ubsan and build-tsan CI builds.

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D5695