x86: Add a testcase for PR target/96861

Add a testcase to verify that -march=skylake-avx512 -mtune=skylake-avx512
generates desired code sequence.

	PR target/96861
	* gcc.target/i386/pr96861.c: New test.

gcc/testsuite/gcc.target/i386/pr96861.c

@@ -0,0 +1,38 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -mstv -march=skylake-avx512 -mtune=skylake-avx512" } */
+
+#define max(a,b) (((a) > (b))? (a) : (b))
+#define min(a,b) (((a) < (b))? (a) : (b))
+
+int smax1(int x)
+{
+  return max(x,1);
+}
+
+int smin1(int x)
+{
+  return min(x,1);
+}
+
+int smaxm1(int x)
+{
+  return max(x,-1);
+}
+
+int sminm1(int x)
+{
+  return min(x,-1);
+}
+
+unsigned int umax1(unsigned int x)
+{
+  return max(x,1);
+}
+
+unsigned int umin1(unsigned int x)
+{
+  return min(x,1);
+}
+
+/* { dg-final { scan-assembler-times "test" 6 } } */
+/* { dg-final { scan-assembler-not "cmp" } } */