link-warning a build-aux file?

[Simon Josefsson]

Hi!  Do we need to put link-warning.h in build-aux/?  Since it is a C
header file, having it in the lib/ directory seems cleaner to me.

(I noticed this because my build-aux directory is '.', so all gnulib
scripts end up in my top-level project directory, which is fine because
there is where the other autoconf scripts are stored, but having a *.h
file there seemed weird.)

/Simon