[libc++] Use ASSERT_SAME_TYPE instead of <type_traits> in depr tests

Whenever, possible, use ASSERT_SAME_TYPE instead of static_assert along
with std::is_same in the depr header tests. This prevents dragging in
multiple headers unrelated to the header being tested, which can (and
has) hidden issues.

Also, add a couple of tests to ensure that basic declarations in
<stddef.h> and <stdint.h> are available when including just those
headers, since the rest of the tests for those types require pulling
in additional dependencies.

Differential Revision: https://reviews.llvm.org/D145116