When running `make format` it will update all files. If a file does not
actually require reformatting, it will trigger a re-build of the entire
code base.
This commit instead compare the re-formatted file with the existing one
and does not update it unless it has actually changed.
We are switching from pgindent to clang-format for several
reasons:
1) pgindent is harder to set up and depends on other tools
like gobjdump that differ between OSes making it harder
to set up a proper development environment.
2) clang-format is more standard and works better
with various IDEs and editors.
Our clang-format wrapper script is transactional in that this
version of the script copies all files to a temporary directory,
runs clang-format in the temp dir, and only then copies the files
back. This should prevent mis-formatting when the script is cancled
in the middle of running.
We changes travis to use clang-format instead of pgindent
and thus it uses a different docker image to do the format test.
We also changes travis to use the new clang docker
image for the license check and prefix checks for consistency.
This also paves the way for us to use more clang features for tests
in the future.
