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/exiv2/default.nix

@@ -69,7 +69,7 @@ stdenv.mkDerivation rec {
     ''}
 
     ${stdenv.lib.optionalString stdenv.isDarwin ''
-      export DYLD_LIBRARY_PATH=$DYLD_LIBRARY_PATH:`pwd`/lib
+      export DYLD_LIBRARY_PATH=$DYLD_LIBRARY_PATH''${DYLD_LIBRARY_PATH:+:}`pwd`/lib
       # Removing tests depending on charset conversion
       substituteInPlace ../test/Makefile --replace "conversions.sh" ""
       rm -f ../tests/bugfixes/redmine/test_issue_460.py