[APInt] Add some procedural APInt::byteSwap unit tests

rGf0181cc7bac3 added specific tests up to i64, this adds a general loop to test some basic byte moves for larger APInts.
diff --git a/llvm/unittests/ADT/APIntTest.cpp b/llvm/unittests/ADT/APIntTest.cpp
index c3a9bda..34efbc5 100644
--- a/llvm/unittests/ADT/APIntTest.cpp
+++ b/llvm/unittests/ADT/APIntTest.cpp
@@ -1821,6 +1821,15 @@
   EXPECT_EQ(0x117700ff, APInt(32, 0xff007711).byteSwap());
   EXPECT_EQ(0x050403020100ULL, APInt(48, 0x000102030405ULL).byteSwap());
   EXPECT_EQ(0xff050403020100aaULL, APInt(64, 0xaa000102030405ffULL).byteSwap());
+
+  for (unsigned N : {16, 32, 48, 64, 80, 96, 112, 128, 256, 1024, 1040}) {
+    for (unsigned I = 0; I < N; I += 8) {
+      APInt X = APInt::getBitsSet(N, I, I + 8);
+      APInt Y = APInt::getBitsSet(N, N - I - 8, N - I);
+      EXPECT_EQ(Y, X.byteSwap());
+      EXPECT_EQ(X, Y.byteSwap());
+    }
+  }
 }
 
 TEST(APIntTest, reverseBits) {