I guess you are looking for a Windows related answer, but on Linux, to detect the prescence of the c based gtk+ libs, which Wx would probably be using, you would just check the contents of the pkgconfig directories. The pkgconfig directories maintain the versions and locations of installed gtk+ libs and headers, which are installed in each library location. So you may need to check all paths in your ENV variable LIBPATH.
Run the command pkg-config (notice the dash) for a commandline tool to search it.
I have no idea where MS Windows puts those files.