treewide: Fix unsafe concatenation of $LD_LIBRARY_PATH

Naive concatenation of $LD_LIBRARY_PATH can result in an empty
colon-delimited segment; this tells glibc to load libraries from the
current directory, which is definitely wrong, and may be a security
vulnerability if the current directory is untrusted.  (See #67234, for
example.)  Fix this throughout the tree.

Signed-off-by: Anders Kaseorg <andersk@mit.edu>

pkgs/development/interpreters/pure/default.nix

@@ -24,7 +24,7 @@ stdenv.mkDerivation rec {
   configureFlags = [ "--enable-release" ];
   doCheck = true;
   checkPhase = ''
-    LD_LIBRARY_PATH=$LD_LIBRARY_PATH:${llvm}/lib make check
+    LD_LIBRARY_PATH=$LD_LIBRARY_PATH''${LD_LIBRARY_PATH:+:}${llvm}/lib make check
   '';
   postInstall = ''
     wrapProgram $out/bin/pure --prefix LD_LIBRARY_PATH : ${llvm}/lib