Switch back to variadic log macros.

Switch back to variadic log macros.

This essentially reverts commit 66cdd5bc99a5 which aimed to make the
dss log facility C89 conform. While this was a worthwhile goal in
2012, it has little value today, since in 2025 we can safely assume
a C99 compliant compiler.

The patch was created with

	git revert -Xours 66cdd5bc

followed by manual tweaks to make it compile again.