add test for vector splat literals (#1119)

Vector splat literals have been introduced recently in LLVM, and the
llvm_util in Alive2 already handles this. However, the test suite misses
coverage for splat literals.

tests/alive-tv/vector/vector-splat-literal.srctgt.ll

@@ -0,0 +1,12 @@
+define <2 x i8> @src(<2 x i8> %x) {
+  %rem.i = srem <2 x i8> %x, splat(i8 2)
+  %cmp.i = icmp slt <2 x i8> %rem.i, zeroinitializer
+  %add.i = select <2 x i1> %cmp.i, <2 x i8> splat(i8 2), <2 x i8> zeroinitializer
+  ret <2 x i8> %add.i
+}
+
+define <2 x i8> @tgt(<2 x i8> %x) {
+  %rem.i = srem <2 x i8> %x, splat(i8 2)
+  %tmp1 = and <2 x i8> %rem.i, splat(i8 2)
+  ret <2 x i8> %tmp1
+}