warning: storage class is not first

This pull request fixes the warning issued by `nvc++`
(the C++ compiler in Nvidia HPC SDK/PGI),
and is similar to pull request #1717.

src/catch2/internal/catch_meta.hpp

@@ -17,9 +17,9 @@ namespace Catch {
     template <typename> struct true_given : std::true_type {};
     struct is_callable_tester {
         template <typename Fun, typename... Args>
-        true_given<decltype(std::declval<Fun>()(std::declval<Args>()...))> static test(int);
+        static true_given<decltype(std::declval<Fun>()(std::declval<Args>()...))> test(int);
         template <typename...>
-        std::false_type static test(...);
+        static std::false_type test(...);
     };
 
     template <typename T>