Add tests for carriage return handling

Author: moosichu

test/compare_output.zig

@@ -529,4 +529,13 @@ pub fn addCases(cases: *tests.CompareOutputContext) void {
         \\debug: free - len: 5
         \\
     );
+
+    cases.add("valid carriage return example", "const io = @import(\"std\").io;\r\n" ++ // Testing CRLF line endings are valid
+        "\r\n" ++
+        "pub \r fn main() void {\r\n" ++ // Testing isolated carriage return as whitespace is valid
+        "    const stdout = io.getStdOut().writer();\r\n" ++
+        "    stdout.print(\\\\A Multiline\r\n" ++ // testing CRLF at end of multiline string line is valid and normalises to \n in the output
+        "                 \\\\String\r\n" ++
+        "                 , .{}) catch unreachable;\r\n" ++
+        "}\r\n", "A Multiline\nString");
 }

test/compile_errors.zig

@@ -174,6 +174,16 @@ pub fn addCases(ctx: *TestContext) !void {
         });
     }
 
+    {
+        const case = ctx.obj("isolated carriage return in multiline string literal", .{});
+        case.backend = .stage2;
+
+        case.addError("const foo = \\\\\test\r\r rogue carriage return\n;", &[_][]const u8{
+            ":1:19: error: expected ';' after declaration",
+            ":1:20: note: invalid byte: '\\r'",
+        });
+    }
+
     {
         const case = ctx.obj("missing semicolon at EOF", .{});
         case.addError(