[clang][Expr][NFC] Fix some doc comments (#159504)

Use proper doc comments here instead of regular comments.

Author: tbaederr

clang/include/clang/AST/Expr.h

@@ -634,8 +634,8 @@ class Expr : public ValueStmt {
 
     EvalStatus() = default;
 
-    // hasSideEffects - Return true if the evaluated expression has
-    // side effects.
+    /// Return true if the evaluated expression has
+    /// side effects.
     bool hasSideEffects() const {
       return HasSideEffects;
     }
@@ -646,8 +646,8 @@ class Expr : public ValueStmt {
     /// Val - This is the value the expression can be folded to.
     APValue Val;
 
-    // isGlobalLValue - Return true if the evaluated lvalue expression
-    // is global.
+    /// Return true if the evaluated lvalue expression
+    /// is global.
     bool isGlobalLValue() const;
   };