testqsort: use SDLTest_TestSuite

[madebr]

The suite now tests sorting int arrays, double arrays, custom struct array and int pointer arrays.

It also tests whether qsort preserves all items.
But because it is very slow (O(n^2)), I've hidden it behind a cli argument (--slow-checks)

Description

Existing Issue(s)

[madebr]

@sezero
I perhaps went a bit crazy with the macro templating, but can you see why clang fails here?

[sezero]

I don't know how -Walloc-size-larger-than works, but maybe the compiler
is confused about type limits ???

9223372036854775807 is INT64_MAX (signed), whereas 18446744073709551615
is UINT64_MAX (unsigned) which correspond to SSIZE_MAX and SIZE_MAX for
x86_64.

I'm certainly reaching here, but, does it change anything if you add a
size_t cast in TEST_QSORT_ARRAY and TEST_ARRAY_LOST_NO_ELEMENTS, e.g.
like:

-        TYPE *copy = SDL_calloc((SIZE), sizeof(TYPE));                              \
+        TYPE *copy = SDL_calloc((size_t)(SIZE), sizeof(TYPE));                      \

[madebr]

-        TYPE *copy = SDL_calloc((SIZE), sizeof(TYPE));                              \
+        TYPE *copy = SDL_calloc((size_t)(SIZE), sizeof(TYPE));                      \

Thanks for the hint!
There was a int -> size_t cast for the arraylen variable. I changed the code to keep it always unsigned.