Correctly set errno on failure and improve the related test.
Previously the malloc test would emit an error message but not
abort if the errno was not as expected on failure. This
was because the return in the null == true case prevented the
check for failed == true at the end of check_result from
being reached. To resolve this just abort immediately as in the
null case.
Also add tests of allocations that are expected to fail for
calloc and malloc.
To make the tests pass we need to set errno in several places,
making sure to keep this off the fast path.
We must also take care not to attempt to zero nullptr in case
of calloc failure.
See microsoft/snmalloc#461 and microsoft/snmalloc#463.
* Add concept of natural alignment to tests.
snmalloc naturally aligns blocks very heavily, so that
the largest power-of-two in the rounded size is the alignment.
This checks that in the test, and provides a method for
finding the natural alignment of a block.
* Improve USE_MALLOC to provide alignment
snmalloc provides a lot of alginment guarantees. This ensures that when
we pass through to the system allocator we still get those alignment
guarantees.
The commit also fixes the tests to work with USE_MALLOC, and builds a
set of unit tests for ctest to check behaviour.
