We use R11F_G11F_B10F for HDR so we should stop checking for compressed
IBL files.
Also, make the glTF sample on web more consistent with the default
settings used by gltf_viewer on native and use venetian_crossroads
instead of syferfontein.
* Turn on shaders optimization by default
Release builds of Filament only work well with optimize shaders,
turning optimizations on by default will help avoid mismatches.
This change also adds -g to disable all optimizations, for debug
builds.
* Use -g on debug builds
* Use -g on debug builds
* Update tutorial_redball.md to remove matc's -O
* Update tutorial_suzanne.md to remove matc's -O
* Use -g in debug builds
Note that the WebGL build uses filameshio, but Android does not. Our
Android samples therefore do not yet understand the compressed format.
For web, I measured the before / after:
```
BEFORE: filament.wasm = 505796, suzanne.filamesh = 521476
AFTER: filament.wasm = 510915, suzanne.filamesh = 333489
```
Issue #558
