(RGUI) Make it possible to change overlays from RGUI
(RGUI) Add opacity overlay setting
(RGUI) Add Overlay Scale option - when downscaling, doesn't seem to
update the hitboxes
Fixup overlay handling in RGUI.

- Fix massive memory leaks and behavior.
- Flush menu stack to input options.
- Display which overlay is used.
- Display (DIR)/(FILE) when overlay is searched for.
- Avoid potential floating point error when incrementing/decrementing
  opacity.
Make overlay_scale logic consistent with overlay_alpha.
Print OVERLAY in menu when selecting one.
Allow user to browse overlays more easily.
Fix overlay input hitbox with scaling.
Remove config path in RGUI.

Wonky, opens a can of worms to change it.
Don't check for FBO when compiling GLES2.

Adds FBO support to ARM/Linux which used quickbuild.
Fix libretro-test-gl build for Pi.
Disallow EGL images when using HW render.
More explicit logging of FBO errors.
(ANDROID) fix ROM load error message on threaded video
remove overlay on ROM load error message
Fix desktop GL build.
Be more explicit about FBO formats.

GLES doesn't support 32-bit FBOs.
They seem to only be exposed via OES_rgb8_rgba8 and ARM_rgba8
extensions.
Fix potential segfault if rgui->info is broken.
Avoid Pi hack.

Derp. Was configured to low GPU RAM split ...
Avoid potential performance regressions.

PSGL uses GL_ARGB_SCE, and not GL_RGBA for one ...
Run thread_frame() even when frame = NULL.

Fixes RGUI on cores which use duping.
Also avoid redundant frame.lock locking.
If thr->frame.updated is false, the lock
cannot possible be held by thread.