The change in r263433 broke the contract of the __rotate functions, by no
longer accepting empty ranges. That means that callers which inlined the
old version of std::rotate (without checks) that end up linking to a new
definition of std::__rotate (also without checks) could perform a divide
by zero and crash.
This restores the old contract of the __rotate overloads.
PR libstdc++/90920 partially revert r263433
* include/bits/stl_algo.h (__rotate): Restore checks for empty ranges.
(rotate): Remove checks.
* testsuite/25_algorithms/rotate/90920.cc: New test.
From-SVN: r272489
