Fix unused variable warnings in release build.

Author: rudkx

lib/ClangImporter/ClangImporter.cpp

@@ -228,6 +228,7 @@ namespace {
         getBufferSize()};
       std::error_code error = llvm::sys::Memory::releaseMappedMemory(memory);
       assert(!error && "failed to deallocate read-only zero-filled memory");
+      (void)error;
     }
 
     ZeroFilledMemoryBuffer(const ZeroFilledMemoryBuffer &) = delete;

lib/Frontend/Frontend.cpp

@@ -580,6 +580,7 @@ void CompilerInstance::performParseOnly() {
   assert((Kind == InputFileKind::IFK_Swift ||
           Kind == InputFileKind::IFK_Swift_Library) &&
          "only supports parsing .swift files");
+  (void)Kind;
 
   auto modImpKind = SourceFile::ImplicitModuleImportKind::None;
 

lib/Sema/CSApply.cpp

@@ -6478,9 +6478,9 @@ Expr *ExprRewriter::finishApply(ApplyExpr *apply, Type openedType,
             ->castTo<ExistentialMetatypeType>()
             ->getInstanceType();
         }
-        auto openedArchetype = openedInstanceTy->castTo<ArchetypeType>();
-        assert(openedArchetype->getOpenedExistentialType()
-                              ->isEqual(existentialInstanceTy));
+        assert(openedInstanceTy->castTo<ArchetypeType>()
+                   ->getOpenedExistentialType()
+                   ->isEqual(existentialInstanceTy));
 
         auto opaqueValue = new (tc.Context)
           OpaqueValueExpr(apply->getLoc(), openedTy);