Log Message:
snes9x: Update to 1.59.2

Changes:

- Count clock cycles to synchronize SA1 with S-CPU properly. Based mostly on
  work by Vitor Vilela.
- Only allow instant IRQ when toggling IRQ. Fixes WWF - Wrestlemania.
- Refactored APU output code to buffer less on the client side. Removed 8-bit,
  Mono, and Reverse Stereo options.
- Consistently handle interlacing when we skip frames.
- Changed APU clock to reflect nominal values for original hardware.
- Fix C4 square instruction regression.

libretro:
- Fix multiline cheats.

GTK+:
- Switch from autotools to Meson build system.
- Readd glFinish option as alternative to glFenceSync.
- Fix size fallthrough with xBRZ filter.
- Fix loading of key bindings with spaces in them and modifier keys used alone.
- Add support for libretro ".slang" shaders to OpenGL driver.
- Use a cleaner onscreen font.
- Trap errors to allow OpenGL <= 2.1 to run again.
- Break display settings up to make it easier to access hardware accel section.