Use /bin/sh for all scripts and make dash compatible.

	* arc-versions.sh: Explicitly choose /bin/sh.
	* build-all.sh: Change == to = in tests throughout.
	* build-elf32.sh: Change == to = in tests throughout.
	* check-results.sh: Change == to = in tests throughout, use
	/bin/sh, not /bin/bash.
	* diff-all.sh: Use /bin/sh, not /bin/bash.
	* diff-tests.sh: Likewise
	* get-ip.sh: Change == to = in tests throughout, use
	/bin/sh, not /bin/bash.