Fix Wii U build on macOS with devkitPPC r50 / GCC 14+

[patters-match]

Summary

• Makefile: TARGET_WII_U was being evaluated after OSX_BUILD in the platform detection chain, causing Wii U cross-compilation builds on macOS to be misidentified as native macOS builds. Reordered so TARGET_WII_U is checked first. Also guards the SHA1SUM assignment to avoid errors when the tool is absent.
• src/pc/audio/audio_sdl2.c: adds missing #include <stdio.h>. Tested with devkitPPC r50; GCC 14+ no longer implicitly pulls it in via other headers.

Additional macOS build notes

The following are required to build on macOS but are not part of this patch:

• macOS ships with GNU make 3.81 (2006), which is too old. Install a newer version via Homebrew and use gmake instead of make:

  brew install make

• The bundled armips tool fails to build from source on macOS. Build it separately from its own repo (which has a proper CMake setup) and install it to PATH, then the tools build will detect and use it automatically:

  git clone --recursive https://github.com/Kingcom/armips /tmp/armips-build
  cd /tmp/armips-build && mkdir build && cd build
  cmake ..
  make
  sudo cp armips /usr/local/bin/

• Build the remaining tools explicitly with Clang, followed by the main build:

  gmake -C tools CC=clang CXX=clang++

• Build the main target, and use this mod to wuhbtool to integrate the boot sound. I used Claude Code to rip the excellent boot screen and icon assets from the previously available .wuhb binary, and Claude was able to extract bootSound.btsnd from the Installer release once I had decrypted the files:

  gmake TARGET_WII_U=1 HIGH_FPS_PC=1 VERSION=us -j$(sysctl -n hw.logicalcpu)
  
  wuhbtool build/us_wiiu/sm64.us.f3dex2e.rpx build/us_wiiu/sm64.us.f3dex2e.wuhb \
    --name="Super Mario 64" \
    --short-name="SM64" \
    --author="AboodXD, AloXado320" \
    --icon=build/us_wiiu/iconTex.tga \
    --tv-image=build/us_wiiu/bootTvTex.tga \
    --drc-image=build/us_wiiu/bootDrcTex.tga \
    --boot-sound=build/us_wiiu/bootSound.btsnd

Test plan

• Wii U cross-compilation build completes on macOS without errors
• macOS build target still works as before (I can't test that on macOS since it has a hard dependency on gcc as semantics, unavailable on Darwin).