make: use older mktemp, more

[vtjnash]

Some mktemp only added -p argument recently for BSD vs. gnu consistency with other arguments, so use abspath instead to emulate it. Use it to make various file builds atomic (particularly those shared between release and debug).]

(Coded by Claude)

[fingolfin]

How about we add a new helper script like this (created via ChatGPT, just to keep it interesting ;-)), stored as, say, atomic_write_if_different.sh somewhere we can easily reach it:

#!/bin/sh
# Atomic write-if-different helper
# Usage: atomic_write_if_different.sh TARGET

set -eu

target=$1
tmp=$(mktemp "${target}.XXXXXX") || exit 1

# Ensure temporary file gets cleaned up on exit or interrupt
cleanup() {
    rm -f "$tmp"
}
trap cleanup EXIT INT TERM HUP

# Read stdin to the temporary file
cat > "$tmp"

# If target does not exist, move new file into place
if [ ! -f "$target" ]; then
    mv "$tmp" "$target"
    trap - EXIT
    exit 0
fi

# Compare old and new; only replace if different
if cmp -s "$tmp" "$target"; then
    # identical
    rm -f "$tmp"
else
    mv "$tmp" "$target"
fi

trap - EXIT
exit 0

Then here we can write

Suggested change

	@TMPFILE=$$(mktemp $(abspath $@.XXXXXX)); \
	sed <'$<' >$$TMPFILE -e 's/@JULIA_SHLIB_SYMBOL_VERSION@/JL_LIBJULIA_$(SOMAJOR)/'; \
	mv $$TMPFILE $@
	sed <'$<' -e 's/@JULIA_SHLIB_SYMBOL_VERSION@/JL_LIBJULIA_$(SOMAJOR)/' \
	| PATH/TO/atomic_write_if_different.sh $@

The result has more comprehensive functionality and is arguably easier to read and maintain -- I think this is more visible in some of the other places.

[vtjnash]

I do like that. We need to be careful though, since half of the places we use this, the "if different" policy should not be applied, while the other half it should be (and a few don't care)