Bug 1714069 - Block Mesa software drivers for HW-WR, r=aosmond

We currently allow software drivers such as `llvmpipe` to run HW-WR -
in nightly and  apparently even in release.
Explicitly make these drivers always use SW-WR instead.

While on it, improve our detection for software drivers in glxtest.
This may become handy for new software drivers such as zink+lavapipe.

Differential Revision: https://phabricator.services.mozilla.com/D116771

toolkit/xre/glxtest.cpp

@@ -538,6 +538,8 @@ static bool get_gles_status(EGLDisplay dpy,
         }
         free(renderDeviceName);
 #endif
+      } else {
+        record_value("MESA_ACCELERATED\nFALSE\n");
       }
     }
   }

widget/gtk/GfxInfo.cpp

@@ -636,6 +636,15 @@ const nsTArray<GfxDriverInfo>& GfxInfo::GetGfxDriverInfo() {
     ////////////////////////////////////
     // FEATURE_WEBRENDER
 
+    // All Mesa software drivers, see FEATURE_WEBRENDER_SOFTWARE
+    APPEND_TO_DRIVER_BLOCKLIST_EXT(
+        OperatingSystem::Linux, ScreenSizeStatus::All, BatteryStatus::All,
+        DesktopEnvironment::All, WindowProtocol::All,
+        DriverVendor::SoftwareMesaAll, DeviceFamily::All,
+        nsIGfxInfo::FEATURE_WEBRENDER, nsIGfxInfo::FEATURE_BLOCKED_DEVICE,
+        DRIVER_COMPARISON_IGNORED, V(0, 0, 0, 0), "FEATURE_FAILURE_SOFTWARE_GL",
+        "");
+
     // Intel Mesa baseline, chosen arbitrarily.
     APPEND_TO_DRIVER_BLOCKLIST(
         OperatingSystem::Linux, DeviceFamily::IntelAll,