util/release/build-release: Update script

- Add more help text.
- Remove braces from variables where the variable is isolated.
- Remove --recurse-submodules from clone.  This breaks on old coreboot
versions.
- Add some whitespace between blocks.
- Fix all shellcheck warnings.
- Verify tar version and fail if it doesn't support --sort.

Change-Id: I4a49df99532d9a92a4a05bceff16f96a4fc3e205
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/16883
Tested-by: build bot (Jenkins)
Reviewed-by: Philipp Deppenwiese <zaolin.daisuki@googlemail.com>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
1 file changed