[qt][mesa] always set rgb visual to 24

newer qt versions might make a rgba fb. this can
interact badly with g3 env when using emulator w/ ui

Change-Id: I25770283104cd6d25290f88afa7170afc3fb6b08
diff --git a/android/emulator/main-emulator.cpp b/android/emulator/main-emulator.cpp
index 0c8b319..4f42ad6 100644
--- a/android/emulator/main-emulator.cpp
+++ b/android/emulator/main-emulator.cpp
@@ -257,6 +257,9 @@
      */
     System::get()->envSet("LC_ALL", "C");
 
+    /* Set MESA_RGB_VISUAL to something that will work on Linux */
+    System::get()->envSet("MESA_RGB_VISUAL", "TrueColor 24");
+
     /* Define ANDROID_EMULATOR_DEBUG to 1 in your environment if you want to
      * see the debug messages from this launcher program.
      */