[gn build] Port fc9821a

Author: llvmgnsyncbot

llvm/utils/gn/secondary/clang/lib/Analysis/FlowSensitive/BUILD.gn

@@ -28,6 +28,7 @@ static_library("FlowSensitive") {
     "DataflowAnalysisContext.cpp",
     "DataflowEnvironment.cpp",
     "DebugSupport.cpp",
+    "Formula.cpp",
     "HTMLLogger.cpp",
     "Logger.cpp",
     "RecordOps.cpp",