Sink all InitializePasses.h includes

This file lists every pass in LLVM, and is included by Pass.h, which is
very popular. Every time we add, remove, or rename a pass in LLVM, it
caused lots of recompilation.

I found this fact by looking at this table, which is sorted by the
number of times a file was changed over the last 100,000 git commits
multiplied by the number of object files that depend on it in the
current checkout:
  recompiles    touches affected_files  header
  342380        95      3604    llvm/include/llvm/ADT/STLExtras.h
  314730        234     1345    llvm/include/llvm/InitializePasses.h
  307036        118     2602    llvm/include/llvm/ADT/APInt.h
  213049        59      3611    llvm/include/llvm/Support/MathExtras.h
  170422        47      3626    llvm/include/llvm/Support/Compiler.h
  162225        45      3605    llvm/include/llvm/ADT/Optional.h
  158319        63      2513    llvm/include/llvm/ADT/Triple.h
  140322        39      3598    llvm/include/llvm/ADT/StringRef.h
  137647        59      2333    llvm/include/llvm/Support/Error.h
  131619        73      1803    llvm/include/llvm/Support/FileSystem.h

Before this change, touching InitializePasses.h would cause 1345 files
to recompile. After this change, touching it only causes 550 compiles in
an incremental rebuild.

Reviewers: bkramer, asbirlea, bollu, jdoerfert

Differential Revision: https://reviews.llvm.org/D70211
diff --git a/llvm/lib/Target/AMDGPU/SIPreAllocateWWMRegs.cpp b/llvm/lib/Target/AMDGPU/SIPreAllocateWWMRegs.cpp
index 6cdd12d..09dfe87 100644
--- a/llvm/lib/Target/AMDGPU/SIPreAllocateWWMRegs.cpp
+++ b/llvm/lib/Target/AMDGPU/SIPreAllocateWWMRegs.cpp
@@ -13,18 +13,19 @@
 
 #include "AMDGPU.h"
 #include "AMDGPUSubtarget.h"
-#include "SIInstrInfo.h"
-#include "SIRegisterInfo.h"
-#include "SIMachineFunctionInfo.h"
 #include "MCTargetDesc/AMDGPUMCTargetDesc.h"
+#include "SIInstrInfo.h"
+#include "SIMachineFunctionInfo.h"
+#include "SIRegisterInfo.h"
 #include "llvm/ADT/PostOrderIterator.h"
-#include "llvm/CodeGen/VirtRegMap.h"
 #include "llvm/CodeGen/LiveInterval.h"
 #include "llvm/CodeGen/LiveIntervals.h"
 #include "llvm/CodeGen/LiveRegMatrix.h"
 #include "llvm/CodeGen/MachineDominators.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
 #include "llvm/CodeGen/RegisterClassInfo.h"
+#include "llvm/CodeGen/VirtRegMap.h"
+#include "llvm/InitializePasses.h"
 
 using namespace llvm;