A couple tweaks in how we build OIIO for OSL's CI (#1505)
A couple tweaks in how we build OIIO for OSL's CI (#1505)

* Use unity build to speed up OIIO build (for sufficiently new OIIO).
* Build OIIO with STOP_ON_WARNING=OFF, so that if a compiler upgrades
  and makes new warnings for OIIO, that doesn't break OSL's CI build.

Signed-off-by: Larry Gritz <f0a1ce6f80112d72f7276457fd261d671b827567@larrygritz.com>
aconty/OpenShadingLanguage,lgritz/OpenShadingLanguage,lgritz/OpenShadingLanguage,aconty/OpenShadingLanguage,aconty/OpenShadingLanguage,aconty/OpenShadingLanguage,lgritz/OpenShadingLanguage,aconty/OpenShadingLanguage,lgritz/OpenShadingLanguage,lgritz/OpenShadingLanguage