build: also link raylib for libcombat

Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: I337a654ffc0dbfab19bdbe68ba9bd9026a6a6964

build.zig

@@ -15,6 +15,7 @@ pub fn build(b: *std.Build) void {
         }),
     });
     combat_lib.addIncludePath(b.path("src"));
+    combat_lib.linkSystemLibrary("raylib");
 
     // C sources (everything except combat, which is now Zig)
     const c_sources = [_][]const u8{