* Handle BSD checksum utilities
The BSDs have different checksum utilities than GNU systems do. If we
don't see the GNU checksum utilities installed, use the BSD ones, as
their output is compatible enough.
Addresses part of GH-14688.
* Prefer GNU touch
BSD touch at least in macOS does not handle local timezone in the
timestamp (like 2024-06-27T10:26:23-03:00). As such, try GNU touch (as
ports systems almost always prefix with g if coreutils is installed) and
prefer that if available. It's not the end of the world though if GNU
touch isn't available, as BSD touch on some systems may support it, and
if it doesn't, then it's just timestamps, nothing too serious.
This patch adds missing newlines, trims multiple redundant final
newlines into a single one, and trims redundant leading newlines.
According to POSIX, a line is a sequence of zero or more non-' <newline>'
characters plus a terminating '<newline>' character. [1] Files should
normally have at least one final newline character.
C89 [2] and later standards [3] mention a final newline:
"A source file that is not empty shall end in a new-line character,
which shall not be immediately preceded by a backslash character."
Although it is not mandatory for all files to have a final newline
fixed, a more consistent and homogeneous approach brings less of commit
differences issues and a better development experience in certain text
editors and IDEs.
[1] http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap03.html#tag_03_206
[2] https://port70.net/~nsz/c/c89/c89-draft.html#2.1.1.2
[3] https://port70.net/~nsz/c/c99/n1256.html#5.1.1.2
