'less' should port to C23 by using function prototypes

[eggert]

One of the changes in the 2023 edition of the C standard is that support for K&R style function definitions has been removed. Since 'less' still uses these, it won't compile on a vanilla C23 compiler. And since nobody cares about pre-C89 compilers any more, the simplest fix is for 'less' to use C89-style function prototypes everywhere. It is 33 years after C89, after all.

GCC optionally warns about these obsolete usages; see attached build transcript.I expect some compilers will start erroring out entirely soon.

lessbug.txt

[gwsw]

I agree that it's time to do this.
Fixed in 76a7805 (less-618).