[ADT][NFC] Silence some misc-unconventional-assign-operator warnings

Author: njames93

llvm/include/llvm/ADT/SmallString.h

@@ -306,9 +306,9 @@ class SmallString : public SmallVector<char, InternalLen> {
   }
 
   // Extra operators.
-  const SmallString &operator=(StringRef RHS) {
-    this->clear();
-    return *this += RHS;
+  SmallString &operator=(StringRef RHS) {
+    this->assign(RHS);
+    return *this;
   }
 
   SmallString &operator+=(StringRef RHS) {

llvm/include/llvm/ADT/SmallVector.h

@@ -925,7 +925,7 @@ class LLVM_GSL_OWNER SmallVector : public SmallVectorImpl<T>,
       SmallVectorImpl<T>::operator=(RHS);
   }
 
-  const SmallVector &operator=(const SmallVector &RHS) {
+  SmallVector &operator=(const SmallVector &RHS) {
     SmallVectorImpl<T>::operator=(RHS);
     return *this;
   }
@@ -940,17 +940,17 @@ class LLVM_GSL_OWNER SmallVector : public SmallVectorImpl<T>,
       SmallVectorImpl<T>::operator=(::std::move(RHS));
   }
 
-  const SmallVector &operator=(SmallVector &&RHS) {
+  SmallVector &operator=(SmallVector &&RHS) {
     SmallVectorImpl<T>::operator=(::std::move(RHS));
     return *this;
   }
 
-  const SmallVector &operator=(SmallVectorImpl<T> &&RHS) {
+  SmallVector &operator=(SmallVectorImpl<T> &&RHS) {
     SmallVectorImpl<T>::operator=(::std::move(RHS));
     return *this;
   }
 
-  const SmallVector &operator=(std::initializer_list<T> IL) {
+  SmallVector &operator=(std::initializer_list<T> IL) {
     this->assign(IL);
     return *this;
   }