Add static assert

Author: mborland

include/boost/decimal/gcc_decimal32.hpp

@@ -34,6 +34,8 @@ BOOST_DECIMAL_EXPORT class gcc_decimal32 final
 
 private:
 
+    static_assert(sizeof(std::decimal::decimal32) == sizeof(std::uint32_t), "Incorrect size detected. std::decimal::decimal32 must be exactly 32 bits");
+
     std::decimal::decimal32 internal_decimal_ {};
 
     // Returns the un-biased (quantum) exponent