libstdc++: Fix -Warray-bounds warning in std::vector<bool> [PR110498]

libstdc++: Fix -Warray-bounds warning in std::vector<bool> [PR110498]

In this case, we need to tell the compiler that the current size is not
larger than the new size so that all the existing elements can be copied
to the new storage. This avoids bogus warnings about overflowing the new
storage when the compiler can't tell that that cannot happen.

We might as well also hoist the loads of begin() and end() before the
allocation too. All callers will have loaded at least begin() before
calling _M_reallocate.

libstdc++-v3/ChangeLog:

	PR libstdc++/110498
	* include/bits/vector.tcc (vector<bool, A>::_M_reallocate):
	Hoist loads of begin() and end() before allocation and use them
	to state an unreachable condition.
	* testsuite/23_containers/vector/bool/capacity/110498.cc: New
	test.

Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>