C++: Fix join in reachesRefParameter by joining with 'getEnd' instead

of 'getANode'.

Before:

Tuple counts for FlowVar::FlowVar::reachesRefParameter_dispred#ff/2@956ac39i after 229ms:
  24806   ~1%     {2} r1 = JOIN FlowVar::FlowVar_internal::parameterIsNonConstReference#f WITH Parameter::Parameter::getFunction_dispred#ff ON FIRST 1 OUTPUT Lhs.0 'p', Rhs.1
  56985   ~3%     {3} r2 = JOIN r1 WITH num#FlowVar::FlowVar_internal::TBlockVar#fff_12#join_rhs ON FIRST 1 OUTPUT Rhs.1 'this', Lhs.0 'p', Lhs.1
  2384489 ~4%     {4} r3 = JOIN r2 WITH FlowVar::FlowVar_internal::getAReachedBlockVarSBB#ff ON FIRST 1 OUTPUT Rhs.1, Lhs.2, Lhs.1 'p', Lhs.0 'this'
  49457   ~0%     {2} r4 = JOIN r3 WITH SubBasicBlocks::SubBasicBlock::getANode_dispred#fb ON FIRST 2 OUTPUT Lhs.3 'this', Lhs.2 'p'
                  return r4

After:

Tuple counts for FlowVar::FlowVar::reachesRefParameter_dispred#ff/2@46f8bfn7 after 32ms:
  24806 ~1%     {2} r1 = JOIN FlowVar::FlowVar_internal::parameterIsNonConstReference#f WITH Parameter::Parameter::getFunction_dispred#ff ON FIRST 1 OUTPUT Lhs.0 'p', Rhs.1
  56985 ~1%     {3} r2 = JOIN r1 WITH num#FlowVar::FlowVar_internal::TBlockVar#fff_12#join_rhs ON FIRST 1 OUTPUT Lhs.1, Lhs.0 'p', Rhs.1 'this'
  56985 ~1%     {3} r3 = JOIN r2 WITH SubBasicBlocks::SubBasicBlock::getEnd_dispred#fb_10#join_rhs ON FIRST 1 OUTPUT Lhs.2 'this', Rhs.1, Lhs.1 'p'
  49457 ~0%     {2} r4 = JOIN r3 WITH FlowVar::FlowVar_internal::getAReachedBlockVarSBB#ff ON FIRST 2 OUTPUT Lhs.0 'this', Lhs.2 'p'
                return r4

Author: MathiasVP

cpp/ql/lib/semmle/code/cpp/dataflow/internal/FlowVar.qll

@@ -435,7 +435,7 @@ module FlowVar_internal {
       parameterIsNonConstReference(p) and
       p = v and
       // This definition reaches the exit node of the function CFG
-      getAReachedBlockVarSBB(this).getANode() = p.getFunction()
+      getAReachedBlockVarSBB(this).getEnd() = p.getFunction()
     }
 
     override predicate definedByInitialValue(StackVariable lsv) {