[libc++] Consistently replace `std::` qualification with `_VSTD::` or nothing. NFCI.

I used a lot of `git grep` to find places where `std::` was being used
outside of comments and assert-messages. There were three outcomes:

- Qualified function calls, e.g. `std::move` becomes `_VSTD::move`.
    This is the most common case.

- Typenames that don't need qualification, e.g. `std::allocator` becomes `allocator`.
    Leaving these as `_VSTD::allocator` would also be fine, but I decided
    that removing the qualification is more consistent with existing practice.

- Names that specifically need un-versioned `std::` qualification,
    or that I wasn't sure about. For example, I didn't touch any code in
    <atomic>, <math.h>, <new>, or any ext/ or experimental/ headers;
    and I didn't touch any instances of `std::type_info`.

In some deduction guides, we were accidentally using `class Alloc = typename std::allocator<T>`,
despite `std::allocator<T>`'s type-ness not being template-dependent.
Because `std::allocator` is a qualified name, this did parse as we intended;
but what we meant was simply `class Alloc = allocator<T>`.

Differential Revision: https://reviews.llvm.org/D92250

1 files changed, 1 insertions, 1 deletions

diff --git a/libcxx/include/bitset b/libcxx/include/bitset
index 0096989..b0340b8 100644
--- a/libcxx/include/bitset
+++ b/libcxx/include/bitset
@@ -380,7 +380,7 @@ unsigned long long
 __bitset<_N_words, _Size>::to_ullong(true_type, true_type) const
 {
     unsigned long long __r = __first_[0];
-    for (std::size_t __i = 1; __i < sizeof(unsigned long long) / sizeof(__storage_type); ++__i)
+    for (size_t __i = 1; __i < sizeof(unsigned long long) / sizeof(__storage_type); ++__i)
         __r |= static_cast<unsigned long long>(__first_[__i]) << (sizeof(__storage_type) * CHAR_BIT);
     return __r;
 }