X86AsmPrinter.h - cleanup includes and forward declarations. NFC.

Reduce X86Subtarget.h/MCCodeEmitter.h/TargetMachine.h includes to forward declarations
Add explicit X86Subtarget.h/TargetMachine.h includes to X86AsmPrinter.cpp/X86MCInstLower.cpp
Remove unused MCSymbol forward declaration

llvm/lib/Target/X86/X86AsmPrinter.cpp

@@ -18,6 +18,7 @@
 #include "TargetInfo/X86TargetInfo.h"
 #include "X86InstrInfo.h"
 #include "X86MachineFunctionInfo.h"
+#include "X86Subtarget.h"
 #include "llvm/BinaryFormat/COFF.h"
 #include "llvm/BinaryFormat/ELF.h"
 #include "llvm/CodeGen/MachineConstantPool.h"
@@ -40,6 +41,8 @@
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/MachineValueType.h"
 #include "llvm/Support/TargetRegistry.h"
+#include "llvm/Target/TargetMachine.h"
+
 using namespace llvm;
 
 X86AsmPrinter::X86AsmPrinter(TargetMachine &TM,

llvm/lib/Target/X86/X86AsmPrinter.h

@@ -9,12 +9,9 @@
 #ifndef LLVM_LIB_TARGET_X86_X86ASMPRINTER_H
 #define LLVM_LIB_TARGET_X86_X86ASMPRINTER_H
 
-#include "X86Subtarget.h"
 #include "llvm/CodeGen/AsmPrinter.h"
 #include "llvm/CodeGen/FaultMaps.h"
 #include "llvm/CodeGen/StackMaps.h"
-#include "llvm/MC/MCCodeEmitter.h"
-#include "llvm/Target/TargetMachine.h"
 
 // Implemented in X86MCInstLower.cpp
 namespace {
@@ -22,8 +19,10 @@ namespace {
 }
 
 namespace llvm {
+class MCCodeEmitter;
 class MCStreamer;
-class MCSymbol;
+class X86Subtarget;
+class TargetMachine;
 
 class LLVM_LIBRARY_VISIBILITY X86AsmPrinter : public AsmPrinter {
   const X86Subtarget *Subtarget = nullptr;

llvm/lib/Target/X86/X86MCInstLower.cpp

@@ -19,6 +19,7 @@
 #include "X86AsmPrinter.h"
 #include "X86RegisterInfo.h"
 #include "X86ShuffleDecodeConstantPool.h"
+#include "X86Subtarget.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/iterator_range.h"