build: add cimgui to build

pkg/cimgui/build.zig

@@ -5,7 +5,7 @@ pub fn build(b: *std.Build) !void {
     const target = b.standardTargetOptions(.{});
     const optimize = b.standardOptimizeOption(.{});
 
-    _ = b.addModule("imgui", .{ .source_file = .{ .path = "main.zig" } });
+    _ = b.addModule("cimgui", .{ .source_file = .{ .path = "main.zig" } });
 
     const imgui = b.dependency("imgui", .{});
     const lib = b.addStaticLibrary(.{

pkg/cimgui/c.zig

@@ -0,0 +1,3 @@
+pub usingnamespace @cImport({
+    @cInclude("cimgui.h");
+});

pkg/cimgui/main.zig

@@ -1 +1,3 @@
+pub const c = @import("c.zig");
+
 test {}