[llvm] Use range-based for loops with llvm::drop_begin (NFC)

(cherry picked from commit 96f14ea)

Author: kazutakahirata

llvm/lib/Bitcode/Writer/ValueEnumerator.cpp

@@ -1108,8 +1108,8 @@ void ValueEnumerator::purgeFunction() {
   /// Remove purged values from the ValueMap.
   for (unsigned i = NumModuleValues, e = Values.size(); i != e; ++i)
     ValueMap.erase(Values[i].first);
-  for (unsigned i = NumModuleMDs, e = MDs.size(); i != e; ++i)
-    MetadataMap.erase(MDs[i]);
+  for (const Metadata *MD : llvm::drop_begin(MDs, NumModuleMDs))
+    MetadataMap.erase(MD);
   for (const BasicBlock *BB : BasicBlocks)
     ValueMap.erase(BB);
 

llvm/lib/TextAPI/RecordsSlice.cpp

@@ -332,9 +332,8 @@ llvm::MachO::convertToInterfaceFile(const Records &Slices) {
   }
 
   File = createInterfaceFile(Slices, *InstallNames.begin());
-  for (auto it = std::next(InstallNames.begin()); it != InstallNames.end();
-       ++it)
-    File->addDocument(createInterfaceFile(Slices, *it));
+  for (StringRef IN : llvm::drop_begin(InstallNames))
+    File->addDocument(createInterfaceFile(Slices, IN));
 
   return File;
 }