[compiler] Explicitly initialize const members

This fixes a compilation error in Node.js with Xcode:

initialize the const member 'blueprint_'.

error: constructor for 'v8::internal::compiler::Callee' must explicitly
Change-Id: Ia55398428d0de35a9ad5132eabd22d0adb694514
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1895561
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64719}

src/compiler/serializer-for-background-compilation.cc

@@ -314,8 +314,10 @@ class CompilationSubject {
 // always has a FunctionBlueprint.
 class Callee {
  public:
-  explicit Callee(Handle<JSFunction> jsfunction) : jsfunction_(jsfunction) {}
-  explicit Callee(FunctionBlueprint const& blueprint) : blueprint_(blueprint) {}
+  explicit Callee(Handle<JSFunction> jsfunction)
+      : jsfunction_(jsfunction), blueprint_() {}
+  explicit Callee(FunctionBlueprint const& blueprint)
+      : jsfunction_(), blueprint_(blueprint) {}
 
   Handle<SharedFunctionInfo> shared(Isolate* isolate) const {
     return blueprint_.has_value()