Mklog parses the diff content from prepare-commit-msg hook but fails
when git has been configured with mnemonicPrefix. Forcing the default
values for the prefixes would set a distinct diff configuration supported
by mklog and prevent most failures.

contrib/ChangeLog:

	* prepare-commit-msg: Force default git prefixes.

Signed-off-by: Pierre-Emmanuel Patry <pierre-emmanuel.patry@embecosm.com>

Consider Signed-off-by lines as part of the ending of the initial
commit to avoid having these in the middle of the log when the
changelog part is injected after.

This is particularly usefull with:

 $ git gcc-commit-mklog --amend -s

that can be used to create the changelog and add the Signed-off-by line.

Also applies most of the shellcheck suggestions on the
prepare-commit-msg hook.

contrib/ChangeLog:

	* mklog.py: Leave SOB lines after changelog.
	* prepare-commit-msg: Apply most shellcheck suggestions.

Signed-off-by: Marc Poulhiès <dkm@kataplop.net>

contrib/ChangeLog:

	* git-commit-mklog.py: Do not parse -b argument.
	Pass mklog_args as json environment variable.
	* mklog.py: Parse GCC_MKLOG_ARGS and append it to sys.argv.
	* prepare-commit-msg: Do not append GCC_MKLOG_ARGS to args.

contrib/ChangeLog:

	* gcc-git-customization.sh: Use the new wrapper.
	* git-commit-mklog.py: New file.
	* prepare-commit-msg: Support GCC_MKLOG_ARGS.

With this change the prepare-commit-msg hook can compare the log of a
commit being amended with the staged changes, and not run mklog.py
unnecessarily. This is controlled by a git config option,
gcc-config.mklog-hook-type.

contrib/ChangeLog:

	* prepare-commit-msg: Use the gcc-config.mklog-hook-type Git
	config key instead of the GCC_FORCE_MKLOG environment variable.
	Optionally disable generating a new ChangeLog template for
	amended commits when the existing log is still OK.

contrib/ChangeLog:

	* prepare-commit-msg: Replace ENV variable with a git config
	value.

contrib/ChangeLog:

	* prepare-commit-msg: Use 'tee' to save the diff to a file
	instead of running 'git diff' twice.