Re-apply r211399, "Generate native unwind info on Win64" with a fix to ignore SEH pseudo ops in X86 JIT emitter.

--
This patch enables LLVM to emit Win64-native unwind info rather than
DWARF CFI.  It handles all corner cases (I hope), including stack
realignment.

Because the unwind info is not flexible enough to describe stack frames
with a gap of unknown size in the middle, such as the one caused by
stack realignment, I modified register spilling code to place all spills
into the fixed frame slots, so that they can be accessed relative to the
frame pointer.

Patch by Vadim Chugunov!

Reviewed By: rnk

Differential Revision: http://reviews.llvm.org/D4081

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211691 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Target/TargetFrameLowering.h

@@ -93,6 +93,19 @@ public:
   /// stack pointer.
   virtual bool isFPCloseToIncomingSP() const { return true; }
 
+  /// assignCalleeSavedSpillSlots - Allows target to override spill slot
+  /// assignment logic.  If implemented, assignCalleeSavedSpillSlots() should
+  /// assign frame slots to all CSI entries and return true.  If this method
+  /// returns false, spill slots will be assigned using generic implementation.
+  /// assignCalleeSavedSpillSlots() may add, delete or rearrange elements of
+  /// CSI.
+  virtual bool
+  assignCalleeSavedSpillSlots(MachineFunction &MF,
+                              const TargetRegisterInfo *TRI,
+                              std::vector<CalleeSavedInfo> &CSI) const {
+    return false;
+  }
+
   /// getCalleeSavedSpillSlots - This method returns a pointer to an array of
   /// pairs, that contains an entry for each callee saved register that must be
   /// spilled to a particular stack location if it is spilled.