fixup! remove use_system_libwayland

Fixes ANGLE build -

ERROR Unresolved dependencies.
//third_party/SwiftShader/src/WSI:WSI(//build/toolchain/linux:clang_x64)
  needs //third_party/SwiftShader/src/WSI:wayland_client(//build/toolchain/linux:clang_x64)

Bug: chromium:1385736
Change-Id: I80cfd0644cee738d0a219bac03882056193cd4de
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/70448
Commit-Queue: Alexis Hétu <sugoi@google.com>
Commit-Queue: Maksim Sisov <msisov@igalia.com>
Tested-by: Alexis Hétu <sugoi@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
diff --git a/src/WSI/BUILD.gn b/src/WSI/BUILD.gn
index f2c7b0a..b86b819 100644
--- a/src/WSI/BUILD.gn
+++ b/src/WSI/BUILD.gn
@@ -87,7 +87,8 @@
     "../Vulkan:swiftshader_libvulkan_headers",
   ]
 
-  if (is_linux && ozone_platform_wayland) {
+  # Do not try to depend on Wayland if the |wayland_gn_dir| is not set.
+  if (is_linux && ozone_platform_wayland && wayland_gn_dir != "") {
     # Use third-party targets
     deps += [ "$wayland_gn_dir:wayland_client" ]
   }