swiftPackages.{sourcekit-lsp,swift-format}: link libdispatch.so

In my experience this solution seems to be necessary on almost all if
not all Swift packages on Linux

pkgs/development/compilers/swift/sourcekit-lsp/default.nix

@@ -7,6 +7,7 @@
   swift,
   swiftpm,
   swiftpm2nix,
+  Dispatch,
   Foundation,
   XCTest,
   sqlite,
@@ -40,6 +41,10 @@ stdenv.mkDerivation {
     ncursesInput
   ];
 
+  env.LD_LIBRARY_PATH = lib.optionalString stdenv.hostPlatform.isLinux (
+    lib.makeLibraryPath [ Dispatch ]
+  );
+
   configurePhase = generated.configure + ''
     swiftpmMakeMutable indexstore-db
     patch -p1 -d .build/checkouts/indexstore-db -i ${./patches/indexstore-db-macos-target.patch}

pkgs/development/compilers/swift/swift-format/default.nix

@@ -6,6 +6,7 @@
   swift,
   swiftpm,
   swiftpm2nix,
+  Dispatch,
   Foundation,
 }:
 let
@@ -24,6 +25,10 @@ stdenv.mkDerivation {
   ];
   buildInputs = [ Foundation ];
 
+  env.LD_LIBRARY_PATH = lib.optionalString stdenv.hostPlatform.isLinux (
+    lib.makeLibraryPath [ Dispatch ]
+  );
+
   configurePhase = generated.configure;
 
   # We only install the swift-format binary, so don't need the other products.