fix expat build issue

```
install
└─ install wayland-scanner
   └─ zig build-exe wayland-scanner Debug native
      └─ zig build-lib expat Debug native
         └─ configure cmake header dependency to expat_config.h failure
error: /home/user/.cache/zig/p/1220ac6fead249f922d08168f43295090ba7d6e7567e0314dc06cf2fb9ce11ed2bea/expat/expat_config.h.cmake:7: unable to substitute variable: error: MissingValue
error: /home/user/.cache/zig/p/1220ac6fead249f922d08168f43295090ba7d6e7567e0314dc06cf2fb9ce11ed2bea/expat/expat_config.h.cmake:120: unable to substitute variable: error: MissingValue
error: /home/user/.cache/zig/p/1220ac6fead249f922d08168f43295090ba7d6e7567e0314dc06cf2fb9ce11ed2bea/expat/expat_config.h.cmake:123: unable to substitute variable: error: MissingValue
error: HeaderConfigFailed
```

Author: jethrodaniel

build/wayland_scanner/build.zig

@@ -34,6 +34,13 @@ pub fn build(b: *std.Build) !void {
             .style = .{ .cmake = expat_dep.path("expat/expat_config.h.cmake") },
             .include_path = "expat_config.h",
         }, .{
+            .BYTEORDER = @as(i64, switch (b.graph.host.result.cpu.arch.endian()) {
+                .little => 1234,
+                .big => 4321,
+            }),
+            .off_t = null,
+            .size_t = "unsigned",
+
             .HAVE_STDLIB_H = 1,
             .HAVE_STRINGS_H = 1,
             .HAVE_STRING_H = 1,