Always export executable symbols, even if it's also readable

Currently, binexplib (used on windows to export symbols from DLLs on windows) skips readable symbols - even if the segment also has the executable/code flags set. This could lead to missing exports from the DLL, and thus to linker errors.

I'm not 100% sure if this change won't export something it shouldn't - but I couldn't think of any executable symbol CMake shouldn't export in the DLL. I'm also not sure if there is any non-executable non-readable symbol which should be exported - so I left the original condition there.