vulkan-loader: Fix MinGW build

- Fix mingwW64 build of vulkan-loader by not including X/wayland libraries on
  windows.

Co-authored-by: Weijia Wang <9713184+wegank@users.noreply.github.com>

pkgs/development/libraries/vulkan-loader/default.nix

@@ -16,7 +16,7 @@ stdenv.mkDerivation rec {
 
   nativeBuildInputs = [ cmake pkg-config ];
   buildInputs = [ vulkan-headers ]
-    ++ lib.optionals (!stdenv.isDarwin) [ libX11 libxcb libXrandr wayland ];
+    ++ lib.optionals stdenv.isLinux [ libX11 libxcb libXrandr wayland ];
 
   cmakeFlags = [ "-DCMAKE_INSTALL_INCLUDEDIR=${vulkan-headers}/include" ]
     ++ lib.optional stdenv.isDarwin "-DSYSCONFDIR=${moltenvk}/share"
@@ -37,7 +37,7 @@ stdenv.mkDerivation rec {
   meta = with lib; {
     description = "LunarG Vulkan loader";
     homepage    = "https://www.lunarg.com";
-    platforms   = platforms.unix;
+    platforms   = platforms.unix ++ platforms.windows;
     license     = licenses.asl20;
     maintainers = [ maintainers.ralith ];
     broken = (version != vulkan-headers.version);

pkgs/development/tools/misc/pkg-config/default.nix

@@ -35,11 +35,11 @@ stdenv.mkDerivation rec {
          "ac_cv_func_posix_getgrgid_r=yes"
        ];
 
-  env.NIX_CFLAGS_COMPILE = builtins.toString (
+  env.NIX_CFLAGS_COMPILE = toString (
     # Silence "incompatible integer to pointer conversion passing 'gsize'" when building with Clang.
-    lib.optionals stdenv.cc.isClang ["-Wno-int-conversion"] ++
+    lib.optionals stdenv.cc.isClang ["-Wno-int-conversion"]
     # Silence fprintf format errors when building for Windows.
-    lib.optionals stdenv.hostPlatform.isWindows ["-Wno-error=format"]
+    ++ lib.optionals stdenv.hostPlatform.isWindows ["-Wno-error=format"]
   );
 
   enableParallelBuilding = true;