[IFS] Fix copy constructor warnings in IFSStub.cpp

[haowei]

Summary

This change fixes the gcc warning on copy constructor in IFSStub.cpp file.

After this patch, gcc-11 no longer show the warning

/llvm/lib/InterfaceStub/IFSStub.cpp: In copy constructor ‘llvm::ifs::IFSStubTriple::IFSStubTriple(const llvm::ifs::IFSStubTriple&)’:
/llvm/lib/InterfaceStub/IFSStub.cpp:32:1: warning: base class ‘struct llvm::ifs::IFSStub’ should be explicitly initialized in the copy constructor [-Wextra]
   32 | IFSStubTriple::IFSStubTriple(IFSStubTriple const &Stub) {
      | ^~~~~~~~~~~~~

[lbenes]

LGTM With gcc-11, I no longer see the warning messages.

llvm/lib/InterfaceStub/IFSStub.cpp

 IFSStub::IFSStub(IFSStub &&Stub) {
   IfsVersion = std::move(Stub.IfsVersion);
   Target = std::move(Stub.Target);
   SoName = std::move(Stub.SoName);
   NeededLibs = std::move(Stub.NeededLibs);
   Symbols = std::move(Stub.Symbols);
 }
 
-IFSStubTriple::IFSStubTriple(IFSStubTriple const &Stub) {
+IFSStubTriple::IFSStubTriple(IFSStubTriple const &Stub) : IFSStub() {
   IfsVersion = Stub.IfsVersion;
   Target = Stub.Target;
   SoName = Stub.SoName;
   NeededLibs = Stub.NeededLibs;
   Symbols = Stub.Symbols;
 }
 
-IFSStubTriple::IFSStubTriple(IFSStub const &Stub) {
+IFSStubTriple::IFSStubTriple(IFSStub const &Stub) : IFSStub() {
   IfsVersion = Stub.IfsVersion;
   Target = Stub.Target;
   SoName = Stub.SoName;
   NeededLibs = Stub.NeededLibs;
   Symbols = Stub.Symbols;
 }
 
 IFSStubTriple::IFSStubTriple(IFSStubTriple &&Stub) {