PR 75964: Invalid integer ABS handling in simplify-rtx.c

PR 75964: Invalid integer ABS handling in simplify-rtx.c

RTL has no distinction between signed and unsigned values, so it
doesn't make sense to test for signed overflow.

2017-05-06  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
	PR rtl-optimization/75964
	* simplify-rtx.c (simplify_const_relational_operation): Remove
	invalid handling of comparisons of integer ABS.

gcc/testsuite/
	PR rtl-optimization/75964
	* gcc.dg/torture/pr75964.c: New test.

From-SVN: r247719