[flang] iwyu fixes after ba7a92c

Author: nico

flang/lib/Lower/PFTBuilder.cpp

@@ -16,6 +16,7 @@
 #include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/IntervalMap.h"
 #include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
 
 #define DEBUG_TYPE "flang-pft"
 

flang/lib/Optimizer/CodeGen/PreCGRewrite.cpp

@@ -19,6 +19,7 @@
 #include "flang/Optimizer/Support/FIRContext.h"
 #include "mlir/Transforms/DialectConversion.h"
 #include "llvm/ADT/STLExtras.h"
+#include "llvm/Support/Debug.h"
 
 //===----------------------------------------------------------------------===//
 // Codegen rewrite: rewriting of subgraphs of ops