Convert PHI getIncomingValue() to foreach over incoming_values().  NFC.

We already had a method to iterate over all the incoming values of a PHI.  This just changes all eligible code to use it.

Ineligible code included anything which cared about the index, or was also trying to get the i'th incoming BB.

llvm-svn: 237169
diff --git a/llvm/lib/Analysis/ConstantFolding.cpp b/llvm/lib/Analysis/ConstantFolding.cpp
index 6a37f95..85a6633 100644
--- a/llvm/lib/Analysis/ConstantFolding.cpp
+++ b/llvm/lib/Analysis/ConstantFolding.cpp
@@ -895,8 +895,7 @@
   if (PHINode *PN = dyn_cast<PHINode>(I)) {
     Constant *CommonValue = nullptr;
 
-    for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
-      Value *Incoming = PN->getIncomingValue(i);
+    for (Value *Incoming : PN->incoming_values()) {
       // If the incoming value is undef then skip it.  Note that while we could
       // skip the value if it is equal to the phi node itself we choose not to
       // because that would break the rule that constant folding only applies if