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/libraries/yder/default.nix

@@ -32,7 +32,7 @@ stdenv.mkDerivation rec {
   doCheck = true;
 
   preCheck = ''
-    export LD_LIBRARY_PATH="$(pwd):$LD_LIBRARY_PATH"
+    export LD_LIBRARY_PATH="$(pwd)''${LD_LIBRARY_PATH:+:}$LD_LIBRARY_PATH"
     export DYLD_FALLBACK_LIBRARY_PATH="$(pwd):$DYLD_FALLBACK_LIBRARY_PATH"
   '';