x86: Add tests for PR tree-optimization/82142

Verify that PR tree-optimization/82142 testcase is properly optimized.

	PR tree-optimization/82142
	* gcc.target/i386/pr82142a.c: New file.
	* gcc.target/i386/pr82142b.c: Likewise.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>