[CodeGen] Avoid GenericDomTreeConstruction.h include in headers (NFC)

This header is split off from GenericDomTree.h so it can be included
in the source file only. Do this for MachineDominators.h and
MachinePostDominators.h.

Author: nikic

llvm/include/llvm/CodeGen/MachineDominators.h

@@ -21,7 +21,6 @@
 #include "llvm/CodeGen/MachineInstr.h"
 #include "llvm/CodeGen/MachineInstrBundleIterator.h"
 #include "llvm/Support/GenericDomTree.h"
-#include "llvm/Support/GenericDomTreeConstruction.h"
 #include <cassert>
 #include <memory>
 #include <optional>

llvm/lib/CodeGen/MachineDominators.cpp

@@ -18,6 +18,7 @@
 #include "llvm/Pass.h"
 #include "llvm/PassRegistry.h"
 #include "llvm/Support/CommandLine.h"
+#include "llvm/Support/GenericDomTreeConstruction.h"
 
 using namespace llvm;
 

llvm/lib/CodeGen/MachinePostDominators.cpp

@@ -13,6 +13,7 @@
 
 #include "llvm/CodeGen/MachinePostDominators.h"
 #include "llvm/InitializePasses.h"
+#include "llvm/Support/GenericDomTreeConstruction.h"
 
 using namespace llvm;
 

llvm/lib/Target/X86/X86FlagsCopyLowering.cpp

@@ -24,6 +24,7 @@
 #include "X86InstrBuilder.h"
 #include "X86InstrInfo.h"
 #include "X86Subtarget.h"
+#include "llvm/ADT/DepthFirstIterator.h"
 #include "llvm/ADT/PostOrderIterator.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/ScopeExit.h"