[Stackmaps] Record the stack size of each function that contains a stackmap/patchpoint intrinsic.

Re-applying the patch, but this time without using AsmPrinter methods.

Reviewed by Andy

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200481 91177308-0d34-0410-b5e6-96231b3b80d8

docs/StackMaps.rst

@@ -314,6 +314,11 @@ format of this section follows:
 .. code-block:: none
 
   uint32 : Reserved (header)
+  uint32 : NumFunctions
+  StkSizeRecord[NumFunctions] {
+    uint32 : Function Offset
+    uint32 : Stack Size
+  }
   uint32 : NumConstants
   Constants[NumConstants] {
     uint64 : LargeConstant