Adding a build-dependency on flex

[Nicolás Alvarez]

Hi devs,

I'm working on some stuff in the CMake parser which involves changes
to the lexer. It's written in flex, and currently taken unmodified
from the CMake project.

We currently ship both the generated code (.c) and the flex source
(.in.l) in the git repository. With current versions of flex, the
.in.l file doesn't even work; and after fixing it, flex unsurprisingly
generates a different .c than we have now.

It's being annoying to have to manually run flex to regenerate the .c
between changing something and running 'make'. I think it would be
better to ship only the .l file and run flex at compile time. But this
would mean adding a required compile-time dependency on flex to
kdevelop. What do you think about it? Is it an acceptable dep to add?
Or should I just continue keeping the .l and .c in sync in every
commit?

-- 
Nicolas