Put libstdc++ on the Nix shell's library path

The shader test links glslang's C++, and under nix develop its binary could
not start: "libstdc++.so.6: cannot open shared object file". The gcc in
buildInputs is the wrapper; the runtime is stdenv.cc.cc.lib, which is now
part of LD_LIBRARY_PATH.

Author: float3

flake.nix

@@ -63,7 +63,10 @@
             # add libraries here (e.g. pkgs.libvmi)
           ];
 
-          LD_LIBRARY_PATH = pkgs.lib.makeLibraryPath (buildInputs ++ nativeBuildInputs);
+          # stdenv.cc.cc.lib is libstdc++.so.6, which the `gcc` above wraps but
+          # does not put here. `cargo test -p site` links glslang's C++ and
+          # cannot start without it.
+          LD_LIBRARY_PATH = pkgs.lib.makeLibraryPath (buildInputs ++ nativeBuildInputs ++ [pkgs.stdenv.cc.cc.lib]);
 
           # Add glibc, clang, glib, and other headers to bindgen search path
           BINDGEN_EXTRA_CLANG_ARGS =