CMakeLists.txt cleanups

[redstar]

Our CMakeLists.txt can be improved in several ways:

• on Windows, there are still unrecognized options from LLVM
• druntime files are compiled 4 times; with a virtual lib this can be reduced to 2 times (debug+optimized)
• support for release and debug builds can be added
• the Gentoo experience can be improved

[dnadlinger]

What do you mean by "druntime files are compiled 4 times"?

[redstar]

Druntime modules are compiled 2 times for druntime.lib and 2 times for phobos.lib. This increases compile time for nothing.

[dnadlinger]

Ah, right. This issue will go away automatically, as we need to properly split druntime and Phobos for shared library support anyway.

[dnadlinger]

See also: #366

[redstar]

Commit 40926ea addresses the Gentoo issue.

[Trass3r]

The files also contain workarounds for ridiculously old CMake versions.
There should be a sensible minimum, imo a very high one.

[dnadlinger]

I'm not sure if we can realistically require more than a low 2.8.x version (2.8 is required right now). People on "stable" Linux distros sometimes use ridiculously old CMake versions (as I learned when building the binary packages on Ubuntu 10.04 LTS, although we probably can switch to 12.04 now).

But yes, there might be some workarounds for 2.6 versions in there, which somebody needs to clean up.

[redstar]

Request from Russel Winder:

I created a brand new build directory for Fedora 20, but had a build
failure. It appears that on Debian, the package llvm-dev installs in all
the static libraries as well as the header files. However on Fedora 20
llvm-devel only installs the header files, you have to install
llvm-static as well to get the static libraries. The CMake files did not
check that the needed static libraries were in place :-( Is it possible
for CMake to make such a check?

(A check to link against the LLVM libaries can be added. Same for libconfig++.)

[dnadlinger]

If Fedora installs a llvm-config that leads to an unbuildable result, that might as well be a Fedora packaging bug, though. Of course, we can still try to detect it if it doesn't add too many complications.

[dnadlinger]

Closing this old umbrella bug, as all the improvements listed seem to be incorporated. Please open a new issue for any further ideas.