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/compilers/halide/default.nix

@@ -29,7 +29,7 @@ in llvmPackages.stdenv.mkDerivation {
   # To handle the lack of 'local' RPATH; required, as they call one of
   # their built binaries requiring their libs, in the build process.
   preBuild = ''
-    export LD_LIBRARY_PATH="$(pwd)/lib:$LD_LIBRARY_PATH"
+    export LD_LIBRARY_PATH="$(pwd)/lib''${LD_LIBRARY_PATH:+:}$LD_LIBRARY_PATH"
   '';
 
   enableParallelBuilding = true;