Build OmpSs-2 LLVM with commit version information

Allows users to see which commit (or git tag) was used in clang.
Examples for the release and git versions:

% clang --version
clang version 18.0.0 (18.0.0-ompss-2)

% clang --version
clang version 18.0.0 (0a6d6c6)

Reviewed-by: Aleix Roca Nonell <aleix.rocanonell@bsc.es>
Tested-by: Rodrigo Arias Mallo <rodrigo.arias@bsc.es>

pkgs/llvm-ompss2/clang.nix

@@ -113,6 +113,8 @@ in stdenv.mkDerivation rec {
       # install
       "-DCMAKE_INSTALL_RPATH_USE_LINK_PATH=ON"
       "-DCMAKE_INSTALL_RPATH=${zlib}/lib:${gcc.cc.lib}/lib"
+      "-DLLVM_APPEND_VC_REV=ON"
+      "-DLLVM_FORCE_VC_REVISION=${source.version}"
     )
   '';