Add environment variable override helper function

This allows FORCE_QT_GLES and SEPARATE_TEST_DECODER to override both true and false.

app/streaming/video/ffmpeg-renderers/genhwaccel.cpp

@@ -1,4 +1,5 @@
 #include "genhwaccel.h"
+#include "utils.h"
 
 GenericHwAccelRenderer::GenericHwAccelRenderer(AVHWDeviceType hwDeviceType)
     : IFFmpegRenderer(RendererType::Unknown),
@@ -56,9 +57,9 @@ bool GenericHwAccelRenderer::isDirectRenderingSupported()
 
 int GenericHwAccelRenderer::getDecoderCapabilities()
 {
-    bool ok;
-    int caps = qEnvironmentVariableIntValue("GENHWACCEL_CAPS", &ok);
-    if (ok) {
+    int caps;
+
+    if (Utils::getEnvironmentVariableOverride("GENHWACCEL_CAPS", &caps)) {
         SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION,
                     "Using GENHWACCEL_CAPS for decoder capabilities: %x",
                     caps);