add webOS to CMakeLists

[cscd98]

Allows building for webOS

[flyinghead]

Does it build?
Has this been tested on any webOS device?

[cscd98]

It compiles as a libretro core using:

cmake ../ -DLIBRETRO=ON -DCMAKE_BUILD_TYPE=Release

I just tried Dead or Alive Demo (I don't have any Saturn games) on my G4 OLED and it just goes to a black screen. I tried both GLES and GLES 2 compiled modes. It's correctly identified architecture as ARM according to my debugging in CMakeLists (I assume the JIT is automatically enabled by taking a quick look at the source?)

I haven't used flycast before, but I tried a pre-compiled core on Ubuntu and that worked fine. I'm maintaining the webOS cores at the moment and doing lots of PRs to fix compilation issues.

Here is a log if its any use:

https://pastebin.com/ALCe5qbB