alacritty: --add-rpath instead of --set-rpath

As reported by @blucoat in
NixOS#219213 alacritty's RPATH is
missing many of the libraries which it links to, including for
example glibc.

The problem was diagnosed by @kchibisov as being caused by
alacritty's use of `--set-rpath` (which completely replaces the
rpath) instead of `--add-rpath` (which adds additional entries to
the rpath):

  NixOS#219213 (comment)

This commit implements @kchibisov's idea to change `--set-rpath` to
`--add-rpath`:

  NixOS#219213 (comment)

Closes NixOS#219213

pkgs/applications/terminal-emulators/alacritty/default.nix

@@ -104,7 +104,7 @@ rustPlatform.buildRustPackage rec {
       # As a workaround, strip manually before running patchelf.
       $STRIP -S $out/bin/alacritty
 
-      patchelf --set-rpath "${lib.makeLibraryPath rpathLibs}" $out/bin/alacritty
+      patchelf --add-rpath "${lib.makeLibraryPath rpathLibs}" $out/bin/alacritty
     ''
   ) + ''