Add comments about the test cases that have been disabled

lib/std/hash/auto_hash.zig

@@ -355,6 +355,7 @@ test "testHash union" {
 }
 
 test "testHash vector" {
+    // Disabled because of #3317
     if (@import("builtin").arch == .mipsel) return error.SkipZigTest;
 
     const a: @Vector(4, u32) = [_]u32{ 1, 2, 3, 4 };

test/stage1/behavior/byteswap.zig

@@ -39,6 +39,7 @@ test "@byteSwap integers" {
 }
 
 test "@byteSwap vectors" {
+    // Disabled because of #3317
     if (@import("builtin").arch == .mipsel) return error.SkipZigTest;
 
     const ByteSwapVectorTest = struct {

test/stage1/behavior/shuffle.zig

@@ -33,6 +33,7 @@ test "@shuffle" {
             expect(mem.eql(i32, ([4]i32)(res), [4]i32{ 2147483647, 3, -2, 4 }));
 
             // bool
+            // Disabled because of #3317
             if (@import("builtin").arch != .mipsel) {
                 var x2: @Vector(4, bool) = [4]bool{ false, true, false, true };
                 var v4: @Vector(2, bool) = [2]bool{ true, false };