Fix issue associated with SVN LLVM.

When compiling the Haskell binding against a SVN version of LLVM, the output of `llvm-config --version` is (for example) `3.0svn`.

This causes the `HS_LLVM_VERSION` variable to become `300svn` and breaks all preprocessor `#if` checks on said variable.

Commit c6d1c5c fixes the issue by stripping the "svn" (or any other suffix) from the version string.