[TargetMachine] Remove DefaultOptions (#66673)

7d81813 says that this was used because functions missing certain
attributes (e.g. fast math) would inherit behavior from previous
functions with those attributes. However, later c378e52 explicitly set
those attributes if they were missing and removed the use of
DefaultOptions.

llvm/include/llvm/Target/TargetMachine.h

@@ -116,7 +116,6 @@ class TargetMachine {
   std::optional<PGOOptions> PGOOption;
 
 public:
-  const TargetOptions DefaultOptions;
   mutable TargetOptions Options;
 
   TargetMachine(const TargetMachine &) = delete;

llvm/lib/Target/TargetMachine.cpp

@@ -35,7 +35,7 @@ TargetMachine::TargetMachine(const Target &T, StringRef DataLayoutString,
     : TheTarget(T), DL(DataLayoutString), TargetTriple(TT),
       TargetCPU(std::string(CPU)), TargetFS(std::string(FS)), AsmInfo(nullptr),
       MRI(nullptr), MII(nullptr), STI(nullptr), RequireStructuredCFG(false),
-      O0WantsFastISel(false), DefaultOptions(Options), Options(Options) {}
+      O0WantsFastISel(false), Options(Options) {}
 
 TargetMachine::~TargetMachine() = default;