[clang][Interp] Call dtor of Floating values

[tbaeder]

Summary

The APFloat might heap-allocate some memory, so we need to call its
destructor.

[aaron.ballman]

LGTM!

clang/lib/AST/Interp/Descriptor.cpp

static BlockCtorFn getCtorPrim(PrimType Type) {
   // constructor called.
   if (Type == PT_Float)
     return ctorTy<PrimConv<PT_Float>::T>;
 
   COMPOSITE_TYPE_SWITCH(Type, return ctorTy<T>, return nullptr);
 }
 
 static BlockDtorFn getDtorPrim(PrimType Type) {
+  // Floating types are special. They are primitives, but need their
+  // destructor called, since they might allocate memory.
+  if (Type == PT_Float)
+    return dtorTy<PrimConv<PT_Float>::T>;
+
   COMPOSITE_TYPE_SWITCH(Type, return dtorTy<T>, return nullptr);
 }
 
 static BlockMoveFn getMovePrim(PrimType Type) {
   COMPOSITE_TYPE_SWITCH(Type, return moveTy<T>, return nullptr);
 }
 
 static BlockCtorFn getCtorArrayPrim(PrimType Type) {

clang/test/AST/Interp/floats.cpp

namespace ZeroInit {
   };
 
   constexpr A<float> a{12};
   static_assert(a.f == 0.0f, "");
 
   constexpr A<double> b{12};
   static_assert(a.f == 0.0, "");
 };
+
+namespace LongDouble {
+  constexpr long double ld = 3.1425926539;
+}