[platform] Add empty platform_base source set (project-chip#34883)

* [platform] Add empty platform_base source set

When cross-compiling on Windows, bootstrap would fail
because of some targets that are depending on platform_base
source set, which is not defined for chip_device_platform None.

Signed-off-by: marius-alex-tache <marius.tache@nxp.com>

* Restyled by gn

---------

Signed-off-by: marius-alex-tache <marius.tache@nxp.com>
Co-authored-by: Restyled.io <commits@restyled.io>

src/platform/BUILD.gn

@@ -611,6 +611,9 @@ if (chip_device_platform != "none") {
   group("platform") {
     public_deps = [ ":platform_buildconfig" ]
   }
+
+  source_set("platform_base") {
+  }
 }
 
 source_set("syscalls_stub") {