ADT: Remove == and != comparisons between ilist iterators and pointers

I missed == and != when I removed implicit conversions between iterators
and pointers in r252380 since they were defined outside ilist_iterator.

Since they depend on getNodePtrUnchecked(), they indirectly rely on UB.
This commit removes all uses of these operators.  (I'll delete the
operators themselves in a separate commit so that it can be easily
reverted if necessary.)

There should be NFC here.

llvm-svn: 261498
diff --git a/llvm/lib/CodeGen/SjLjEHPrepare.cpp b/llvm/lib/CodeGen/SjLjEHPrepare.cpp
index daf32e4..ce01c5f 100644
--- a/llvm/lib/CodeGen/SjLjEHPrepare.cpp
+++ b/llvm/lib/CodeGen/SjLjEHPrepare.cpp
@@ -419,7 +419,7 @@
   // directly to the caller's context, which is what we want anyway, so no need
   // to do anything here.
   for (BasicBlock &BB : F) {
-    if (&BB == F.begin())
+    if (&BB == &F.front())
       continue;
     for (Instruction &I : BB)
       if (I.mayThrow())
@@ -434,7 +434,7 @@
   // Following any allocas not in the entry block, update the saved SP in the
   // jmpbuf to the new value.
   for (BasicBlock &BB : F) {
-    if (&BB == F.begin())
+    if (&BB == &F.front())
       continue;
     for (Instruction &I : BB) {
       if (auto *CI = dyn_cast<CallInst>(&I)) {