Bug 1777910 - Adjust Mesa environment variables for change/deprecation in 22.1. r=gcp

Mesa 22.1.0 changed the env var name MESA_GLSL_CACHE_DISABLE to
MESA_SHADER_CACHE_DISABLE; it still accepts the old name, but prints a
deprecation warning.  If we set both env vars, then we can support both
old and new Mesas correctly (the warning won't be printed if the new env
var is also set).

Differential Revision: https://phabricator.services.mozilla.com/D151094

ipc/glue/GeckoChildProcessHost.cpp

@@ -427,6 +427,7 @@ GeckoChildProcessHost::GeckoChildProcessHost(GeckoProcessType aProcessType,
     // with sandboxing.  Because we shouldn't need shader caching in
     // this process, we just disable the cache to prevent that.
     mLaunchOptions->env_map["MESA_GLSL_CACHE_DISABLE"] = "true";
+    mLaunchOptions->env_map["MESA_SHADER_CACHE_DISABLE"] = "true";
   }
 #endif
 #if defined(MOZ_ENABLE_FORKSERVER)