[gn build] Port 8918d35

Author: llvmgnsyncbot

llvm/utils/gn/secondary/clang/lib/Basic/BUILD.gn

@@ -61,6 +61,7 @@ static_library("Basic") {
   ]
   include_dirs = [ "." ]
   sources = [
+    "ASTSourceDescriptor.cpp",
     "Attributes.cpp",
     "Builtins.cpp",
     "CLWarnings.cpp",