Export of internal Abseil changes

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2ba0e41a21fbdab36b2f4f3b0dd4b112bd788604 by Derek Mauro <dmauro@google.com>:

Remove the include of <intsafe.h>, which is missing on
some versions of MinGW. DWORD is easily replaced by uint32_t.

PiperOrigin-RevId: 282576177

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238fd41114b3e83fcb91d2afe1e6dcce7cfd53b0 by Samuel Benzaquen <sbenza@google.com>:

Remove assertion in erase(iterator) that tries to use the comparator.
Add missing this-> qualifier.
Fix bug where node elements are not being destroyed properly.

PiperOrigin-RevId: 282427096

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6b9446e3b38ed97451c010933e86a572ab659ab2 by Derek Mauro <dmauro@google.com>:

Improves/fixes feature detection in thread_identity

Only use ABSL_PER_THREAD_TLS_KEYWORD when it is supported (previously
on some platforms it evaluated to nothing, which completely breaks
everything), but prefer it to thread_local since benchmarks indicate
it is slightly faster in this critical code path.

Disable the calls to pthread_sigmask on MinGW where it is not
supported.

PiperOrigin-RevId: 282425291
GitOrigin-RevId: 2ba0e41a21fbdab36b2f4f3b0dd4b112bd788604
Change-Id: I34073ecbb4a43ad71f54161c136d88fc728888f1

absl/container/internal/btree.h

@@ -2031,7 +2031,6 @@ auto btree<P>::erase(iterator iter) -> iterator {
     iterator internal_iter(iter);
     --iter;
     assert(iter.node->leaf());
-    assert(!compare_keys(internal_iter.key(), iter.key()));
     params_type::move(mutable_allocator(), iter.node->slot(iter.position),
                       internal_iter.node->slot(internal_iter.position));
     internal_delete = true;