[ADT] Use a range-based for loop instead of llvm::for_each (NFC)

LLVM Coding Standards discourages llvm::for_each unless we already
have a callable.

Author: kazutakahirata

llvm/include/llvm/ADT/CombinationGenerator.h

@@ -118,10 +118,9 @@ class CombinationGenerator {
       : VariablesChoices(VariablesChoices_) {
 #ifndef NDEBUG
     assert(!VariablesChoices.empty() && "There should be some variables.");
-    llvm::for_each(VariablesChoices, [](ArrayRef<choice_type> VariableChoices) {
+    for (ArrayRef<choice_type> VariableChoices : VariablesChoices)
       assert(!VariableChoices.empty() &&
              "There must always be some choice, at least a placeholder one.");
-    });
 #endif
   }