Comment # 9 on bug 1119186 from Wolfgang Bauer

(In reply to Luca Beltrame from comment #7)
> Likely yes, starting from 5.3. It actually prints a message to stdout saying
> it can't find them. Of course, easy to miss.

I am using kdevelop 5.3.0 on Leap 15.0, and I see no problem or that message
here without clang-devel (or clang5-devel) installed.

So it seems to be caused by a change in clang...

Anyway, if it is needed, we should of course add a Requires to the kdevelop5
package.
I'll take care of that, maybe together with the 5.3.1 update I already prepared
(I'm just waiting for the announcement before I submit it...)

PS: the include files are part of the clang package itself in Leap 15.0:
$ rpm -qf /usr/lib64/clang/5.0.1/include/
clang5-5.0.1-lp150.7.3.1.x86_64

Although, I'm not sure that's being installed by default either. The only
packages that requires it on my system are libqt5-qttools-doc and
kdevelop5-plugin-clang-tidy.