[turbofan] Build s/NULL/nullptr/g and CHECK(x != nullptr) to CHECK_NOT_NULL(x).

src/compiler/mips/instruction-selector-mips.cc

Index: src/compiler/mips/instruction-selector-mips.cc
diff --git a/src/compiler/mips/instruction-selector-mips.cc b/src/compiler/mips/instruction-selector-mips.cc
index 45a1910e7874262708f92059423aaacc1935f998..61cea76b22cc5c9a4f8a9c9f9250a3bfa7f80478 100644
--- a/src/compiler/mips/instruction-selector-mips.cc
+++ b/src/compiler/mips/instruction-selector-mips.cc
@@ -1109,7 +1109,7 @@ void VisitWordCompareZero(InstructionSelector* selector, Node* user,
         if (ProjectionIndexOf(value->op()) == 1u) {
           // We cannot combine the <Operation>WithOverflow with this branch
           // unless the 0th projection (the use of the actual value of the
-          // <Operation> is either NULL, which means there's no use of the
+          // <Operation> is either nullptr, which means there's no use of the
           // actual value, or was already defined, which means it is scheduled
           // *AFTER* this branch).
           Node* const node = value->InputAt(0);