[PR tree-optimization/107312] Make range_true_and_false work with 1-bit signed types.

[PR tree-optimization/107312] Make range_true_and_false work with 1-bit signed types.

range_true_and_false() returns a range of [0,1], which for a 1-bit
signed integer gets passed to the irange setter as [0, -1].  These
endpoints are out of order and cause an ICE.  Through some dumb luck,
the legacy code swaps out of order endpoints, because old VRP would
sometimes pass endpoints reversed, depending on the setter to fix
them.  This swapping does not happen for non-legacy, hence the ICE.

The right thing to do (apart from killing legacy and 1-bit signed
integers ;-)), is to avoid passing out of order endpoints for 1-bit
signed integers.  For that matter, a range of [-1, 0] (signed) or
[0, 1] (unsigned) is just varying.

	PR tree-optimization/107312

gcc/ChangeLog:

	* range.h (range_true_and_false): Special case 1-bit signed types.
	* value-range.cc (range_tests_misc): New test.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/pr107312.c: New test.