Does the folder C:\wxWidgets-2.9.1\lib\gcc_dll contain the library wxmsw29ud?
If not, please fix the path, remove the library or compile the library if it is needed.
Note: I have no reason to believe your hello world requires wxWidgets 2.9 Unicode Debug Library. Do you?
Edit: Please learn the different between Compiler Errors, Linker errors, and Logic errors.
(I did not see any Logic Errors; but any big program tends to have a few till the program works right.)
In the long term this will help you a lot with programming in C.
Tim S.