gltfio: Allow compile-time override of GLTFIO_USE_FILESYSTEM (#9733)

BUGS=486954356

filament/backend/test/test_Autoresolve.cpp

@@ -18,6 +18,7 @@
 
 #include "Shader.h"
 #include "SharedShaders.h"
+#include "Skip.h"
 #include "TrianglePrimitive.h"
 
 #include <backend/PixelBufferDescriptor.h>
@@ -31,6 +32,9 @@ using namespace filament::backend;
 using namespace filament::math;
 
 TEST_F(BackendTest, AutoresolveDifferingSampleCounts) {
+    SKIP_IF(SkipEnvironment(OperatingSystem::CI, Backend::OPENGL), "see b/486954356");
+    SKIP_IF(SkipEnvironment(OperatingSystem::CI, Backend::VULKAN), "see b/486954356");
+
     auto& api = getDriverApi();
     constexpr int kRenderTargetSize = 512;
 

filament/src/details/Engine.cpp

@@ -798,6 +798,12 @@ void FEngine::submitFrame() {
 void FEngine::flush() {
     // flush the command buffer
     flushCommandBuffer(mCommandBufferQueue);
+    
+    // In single-threaded mode, we have to call execute() to drain the command
+    // buffer to really free up space
+    if constexpr (!UTILS_HAS_THREADING) {
+        execute();
+    }
 }
 
 void FEngine::flushAndWait() {

libs/gltfio/src/FFilamentAsset.h

@@ -60,11 +60,13 @@
 #define GLTFIO_WARN(msg) slog.w << msg << io::endl
 #endif
 
+#ifndef GLTFIO_USE_FILESYSTEM
 #if defined(__EMSCRIPTEN__) || defined(__ANDROID__) || defined(FILAMENT_IOS)
 #define GLTFIO_USE_FILESYSTEM 0
 #else
 #define GLTFIO_USE_FILESYSTEM 1
 #endif
+#endif
 
 namespace utils {
     class NameComponentManager;