Make NumOperands and getNumOperands types be consistent.

[trixirt]

Summary

The problem with the compiler never finishing compiling a very large file was tracked down to an overflow of NumOperands.

The element was unsigned short, but it was assigned to by unsigned int in at least the SelectionDAG::createOperands method.
If one builds with -Weverything, the warning is

../include/llvm/CodeGen/SelectionDAG.h:347:30: warning: implicit conversion loses integer precision: 'size_t' (aka 'unsigned long') to 'unsigned short' [-Wconversion]

It was noted that the next element NumValues has a similar issue, but I do not have a test case to prove that.
The test case i do have is proprietary source and resists being reduced because the problem is that the compile never finishes.

include/llvm/CodeGen/SelectionDAGNodes.h

   /// The types of the values this node defines.  SDNode's may
   /// define multiple values simultaneously.
   const EVT *ValueList;
 
   /// List of uses for this SDNode.
   SDUse *UseList = nullptr;
 
   /// The number of entries in the Operand/Value list.
-  unsigned short NumOperands = 0;
+  unsigned NumOperands = 0;
   unsigned short NumValues;
 
   // The ordering of the SDNodes. It roughly corresponds to the ordering of the
   // original LLVM instructions.
   // This is used for turning off scheduling, because we'll forgo
   // the normal scheduling algorithms and output the instructions according to
   // this ordering.
   unsigned IROrder;