build: Fix BUILD.gn build error (#4948)

diff --git a/BUILD.gn b/BUILD.gn
index 4f1c43e..b7e20b3 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -526,7 +526,7 @@
     "source/val/validate_memory.cpp",
     "source/val/validate_memory_semantics.cpp",
     "source/val/validate_memory_semantics.h",
-    "source/val/validate_mesh_shading.h",
+    "source/val/validate_mesh_shading.cpp",
     "source/val/validate_misc.cpp",
     "source/val/validate_mode_setting.cpp",
     "source/val/validate_non_uniform.cpp",