[clang] Complete the revert of 1a14ef1 (#138341)

When merging the fix for FEM_Indeterminate I reverted the follow on
warning fixes, but misread this diff and retained the explicitly
defaulted constructor.

Author: ojhunt

clang/include/clang/Basic/LangOptions.h

@@ -76,8 +76,6 @@ class LangOptionsBase {
   using RoundingMode = llvm::RoundingMode;
   using CFBranchLabelSchemeKind = clang::CFBranchLabelSchemeKind;
 
-  LangOptionsBase() = default;
-
   enum GCMode { NonGC, GCOnly, HybridGC };
   enum StackProtectorMode { SSPOff, SSPOn, SSPStrong, SSPReq };