SolarisStudio considers 'auto' to be a storage class specifier in
C++98 mode (as appropriate), and considers variables without a specified
type to be of type int.  So, it treats

 auto x = 3.14;

as

 auto int x = 3.14;

which in C++98 mode is equivalent to

 int x = 3.14;

and it does not fail to compile as expected.

Change the test to use a reference so that the type must be known.