Fighting with building Blender on Fedora 20 (http://stackoverflow.com/questions/24327680/building-blender-on-fedora-20-osl-compilation-failing-due-to-llvm-clang-mismat) I discovered the following:

Within install_deps.sh the corresponding CLANG sources for any respective LLVM version are obtained through the following logic:

--ver-llvm=x.x.x (optionally as a shell parameter, otherwise defaults to values below)
LLVM_VERSION="3.3"
LLVM_VERSION_MIN="3.3"
...
LLVM_CLANG_SOURCE="http://llvm.org/releases/$LLVM_VERSION/clang-$LLVM_VERSION.src.tar.gz"
...
wget -c $LLVM_CLANG_SOURCE -O "$_src_clang.tar.gz"

This was probably introduced somewhere around the release of LLVM 3.0, where this url naming scheme first shows up (See http://llvm.org/releases/download.html), but for whatever reasons, versions 3.3, 3.4.1 and 3.4.2 use a different naming scheme (cfe-x.x.x.src.tar.gz instead of clang-x.x.x.src.tar.gz), thus everyone who runs install_deps.sh for these LLVM versions (and by default most people should in fact be running it for 3.3) obtains no CLANG at all (a 0 byte file is downloaded in these error cases, compilation silently does not occur, no errors whatsoever as far as i have seen), and the success of the build process depends fully on another CLANG being present on system level.

Writing a fix isn't really the problem here, but as there are multiple ways we could deal with this, especially how to handle the uncertainty on the naming scheme for future CLANG releases, I thought I'd bring it up for review and discussion first.