modules/windows: Don't make extra_build_paths relative to @BUILD_ROOT@

These should be relative to the current working directory. If they need
to be absolute when converted to strings, the caller should use
`.abs_string_list()` to convert them.

mesonbuild/modules/windows.py

diff --git a/mesonbuild/modules/windows.py b/mesonbuild/modules/windows.py
index 60759d4..e47e643 100644
--- a/mesonbuild/modules/windows.py
+++ b/mesonbuild/modules/windows.py
@@ -119,7 +119,7 @@
         for d in wrc_depends:
             if isinstance(d, build.CustomTarget):
                 extra_args += state.get_include_args([
-                    build.IncludeDirs('', [], False, [os.path.join('@BUILD_ROOT@', self.interpreter.backend.get_target_dir(d))])
+                    build.IncludeDirs('', [], False, [self.interpreter.backend.get_target_dir(d)])
                 ])
         extra_args += state.get_include_args(kwargs['include_directories'])