Revert "Use slice syntax instead of slice_to, etc."

This reverts commit 40b9f5ded50ac4ce8c9323921ec556ad611af6b7.
I am bad at math
extra comment about macros

Fixes #17190
alloc: fix reallocate_inplace implementation

The returned size is the new real size of the allocation.
native: fix passing errno to parent after fork

The bitshifts were wrong in that they invoked undefined behavior and
only passed the lower byte of the presumed-to-be-32bit errno value.
Apparently all actually possible values for errno happen to be easily
under 256, so this didn't cause any actual problems.

This commit fixes the bitshifts, but doesn't generalize to errno types
that aren't 32bit.
Fix cross-crate tuple structs in statics

Fixes #17169.
Fixes #17649.
std: Help diagnose a flaky test

This test has recently been failing on the bots, and I'm not entirely sure why.
I haven't been able to reproduce locally or on the bots, so I'm adding some
messages to help diagnose the problem hopefully.
Add tests for a few resolved issues
travis: Stop building and testing rust

Instead, only run `make tidy`. The tidy script can run quite quickly, and it's
super annoying to run tests for 50 minutes only to have bors fail with a
"trailing whitespace" error.
rollup merge of #17715 : aturon/revert-slice-ops-libs
rollup merge of #17719 : alexcrichton/diagnose
rollup merge of #16993 : dschatzberg/items-bounds
rollup merge of #17646 : bkoropoff/cast-ice
rollup merge of #17682 : nodakai/librustc-handy-version
rollup merge of #17686 : lucidd/fix
rollup merge of #17695 : steveklabnik/various_docs
rollup merge of #17698 : jistr/guide_export
rollup merge of #17702 : nick29581/enable-dots-test
rollup merge of #17705 : thestinger/realloc
rollup merge of #17706 : thestinger/supp