[gumbo, litehtml] fix dupplicate gumbo symbols

[rioki]

1. Fixes duplicate gumbo symbols introduced by PR#[litehtml] new port version 0.6 #29673
2. Fixes gumbo CMake include folder exports

And because I am an external contributor:

• Changes where crosschecked with other gumbo users (libmupdf)
• Changes comply with the maintainer guide
• The version database is fixed by rerunning ./vcpkg x-add-version --all and committing the result.

[rioki]

I don't understand how qttools is now failing, but I am looking into it.

[JonLiu1993]

@rioki, Please get failure logs here. Please ping me if you need any help.

[rioki]

@JonLiu1993 Thank you. I already found the failure logs; unfortunately this is not the first time I threw the vcpkg CI. My confusion came from the fact that it worked fine on my machine. But after a git clean and rebuild I now have the same issue locally. I am still confused how it broke, but I will soon find out.

[BillyONeal]

Thanks for the fix!