Update assert on SymbolicValue size (#27515)

Since the storage is a multiple of uint64_t (derived by what LLVM's APInt does) we want to check for 2*uin64_t here, even on 32bit platforms.

Author: uraimo

include/swift/SIL/SILConstants.h

@@ -556,7 +556,7 @@ class SymbolicValue {
   void dump() const;
 };
 
-static_assert(sizeof(SymbolicValue) == 2 * sizeof(void *),
+static_assert(sizeof(SymbolicValue) == 2 * sizeof(uint64_t),
               "SymbolicValue should stay small");
 static_assert(std::is_pod<SymbolicValue>::value,
               "SymbolicValue should stay POD");