Add an option to the build_cmake.sh to skip the build phase

Summary:
This will allow for running the configuration phase (cmake) only and
skip the build phase (ninja).

Test Plan:

./build_cmake --no-build

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D7360