incremental: fix enum resolution bugs

test/incremental/change_enum_tag_type

@@ -0,0 +1,59 @@
+#target=x86_64-linux-selfhosted
+#target=x86_64-linux-cbe
+#target=x86_64-windows-cbe
+#target=wasm32-wasi-selfhosted
+#update=initial version
+#file=main.zig
+const Tag = u2;
+const Foo = enum(Tag) {
+    a,
+    b,
+    c,
+    d,
+};
+pub fn main() !void {
+    var val: Foo = undefined;
+    val = .a;
+    try std.io.getStdOut().writer().print("{s}\n", .{@tagName(val)});
+}
+const std = @import("std");
+#expect_stdout="a\n"
+#update=too many enum fields
+#file=main.zig
+const Tag = u2;
+const Foo = enum(Tag) {
+    a,
+    b,
+    c,
+    d,
+    e,
+};
+pub fn main() !void {
+    var val: Foo = undefined;
+    val = .a;
+    try std.io.getStdOut().writer().print("{s}\n", .{@tagName(val)});
+}
+comptime {
+    // These can't be true at the same time; analysis should stop as soon as it sees `Foo`
+    std.debug.assert(@intFromEnum(Foo.e) == 4);
+    std.debug.assert(@TypeOf(@intFromEnum(Foo.e)) == Tag);
+}
+const std = @import("std");
+#expect_error=ignored
+#update=increase tag size
+#file=main.zig
+const Tag = u3;
+const Foo = enum(Tag) {
+    a,
+    b,
+    c,
+    d,
+    e,
+};
+pub fn main() !void {
+    var val: Foo = undefined;
+    val = .a;
+    try std.io.getStdOut().writer().print("{s}\n", .{@tagName(val)});
+}
+const std = @import("std");
+#expect_stdout="a\n"