Please support clang

[toge]

I met a compilation error on clang 13.

In file included from include/seq/devector.hpp:32:
include/seq/type_traits.hpp:43:9: error: redefinition of 'is_trivially_copyable'
        struct is_trivially_copyable
               ^
/usr/local/bin/../lib/gcc/x86_64-linux-gnu/10.3.0/../../../../include/c++/10.3.0/type_traits:676:12: note: previous definition is here
    struct is_trivially_copyable
           ^
In file included from /home/conan/workspace/prod-v1/bsr/cci-3b6fc35d/recipes/seq/all/test_package/test_package.cpp:2:
In file included from include/seq/devector.hpp:32:
include/seq/type_traits.hpp:49:9: error: redefinition of 'is_trivially_move_assignable'
        struct is_trivially_move_assignable : is_trivially_copyable<T> {};
               ^
/usr/local/bin/../lib/gcc/x86_64-linux-gnu/10.3.0/../../../../include/c++/10.3.0/type_traits:1318:12: note: previous definition is here
    struct is_trivially_move_assignable
           ^

This is caused by the is_trivially_copyable condition.
The __GNUG__ and __GNUC__ macros are defined in clang as well as gcc.
The presence of the __clang__ macro should be checked to distinguish it from gcc.

[Thermadiag]

Hi, thanks for the fix! Odly, it works with ClangCl...

[toge]

Thanks!