[libc++][test] Uses qualified std::uint32_t.

The module std does not provide c-types in the global namespace. This
means all these types need to be fully qualified. This is a first step
to convert them by using sed.

Since this is an automated conversion other types like uint64_t are kept
as is.

Note that tests in the directory libcxx/test/std/depr/depr.c.headers
should not be converted automatically. This requires manual attention,
there some test require testing uint32_t in the global namespace. These
test should fail when using the std module, and pass when using the
std.compat module.

A similar issue occurs with atomic, atomic_uint32_t is specified as
  using atomic_uint32_t = atomic<uint32_t>; // freestanding
So here too we need to keep the name in the global namespace in the
tests.

Reviewed By: ldionne, #libc

Differential Revision: https://reviews.llvm.org/D145520