I'm working on a free software (bsd license) project with others. We're searching for a system that check out our source code (svn) and build it also as test it (unit tests with Check / other tools).
It should have a webbased interface and generate reports.
I hope we don't have to write such a system from null by ourselves...
I don't think that there's a buildsystem that is capable of doing all this tasks - but what about combining them?
SCons is a nice buildsystem that runs on every machine that has Python. It can even build directly from SVN. For automatic building you can try Buildbot.
You surely do not have to code this yourself - there are a lot of continuous integration systems which are able to check out source code from systems such as SVN and they are generally easy to extend with your own tasks, so running custom test scripts/programs should not be a problem.
While these CI systems are probably not written in C, this does not matter, since they just need to be able to access and compile your source code, for which they will use an external compiler anyways.
Just to list some of the well known CI tools:
You might also be interested in other questions on Stack Overflow tagged as continuous-integration. :)
My vote would be CruiseControl.NET, it has everything you are asking for. It is open source so the costs are low, and it has a very active user community on google groups to help you with your problems as you grow accustomed to it. Also, although .NET based, using MONO it is very nice on Linux and Mac build servers as well so you have everything covered.