You need to use https://cgit.freedesktop.org/xorg/proto/xorgproto now.

I see.  Thanks.

Having pointer in randrproto git to newly required xorgproto (and nothing else), would have been helpful.

Xserver depending on specific version of xorgproto (which provides now all these headers), instead of there being separate pgkconfig file & check for each of the headers, would IMHO make this transition a lot clearer to everybody who doesn't follow X mailing lists.

(Google searches on randrproto 1.6 returning hits to Keith's patches, which update randrproto to 1.6.0 instead of xorgproto, does not help.)

*** Bug 105295 has been marked as a duplicate of this bug. ***

I built and installed xorgproto, reinstalled xserver and tried building.   I get the same error (in fact grepping the xerver tree for xorgproto trns up nothing).

I also get the same error; in fact this is why I logged in just now, after I tried to compile xorg-server and failed.

I built xorgproto-2018.4 into /usr/ prefix. No error was reported.

The comment by Michel Dänzer is appreciated but I do not think it is enough (to provide information as to what we have to do in order to compile it).

If randrproto is indeed outdated, yet xorgproto is the successor, then perhaps the configure check could prioritize on xorgproto, for systems where the user may have both randrproto and xorgproto compiled.

Check that it really got installed there and all expected files are there, and that you had configured your build environment so that X server configure finds them (check you config.log).

Xorgproto is the repository name, it provides exactly the same pkgconfig things as the separate projects did, as you can see:
https://cgit.freedesktop.org/xorg/proto/xorgproto/tree/

(It's a great change, earlier there were a dozen different repos one needed to pull and build which was ridiculous as they each contained just a header, now one needs to pull & build just one repo to get up to date versions of those pkgconfig & header files.)