macOS build broken with current Xcode CLT: SDL 2.30.2 fails to compile (SDL_cocoawindow.m forward-declaration error)

[bitcoin3us]

Summary

builder/unix.py checks out SDL release-2.30.2 during unix/macOS builds:

cmd_ = ['cd lib/SDL && git checkout release-2.30.2']

SDL 2.30.2 no longer compiles on macOS with current Xcode Command Line Tools (the macOS 26 SDK toolchain):

src/video/cocoa/SDL_cocoawindow.m:938:14: error: receiver type 'SDLOpenGLContext'
for instance message is a forward declaration
            [context movedToNewScreen];

Cause

The SDL build here uses SDL_OPENGL=OFF. With OpenGL off, SDLOpenGLContext's @interface (guarded by SDL_VIDEO_OPENGL_CGL in SDL_cocoaopengl.h) is never compiled — only the @class forward declaration in SDL_cocoawindow.h — while windowDidChangeScreen: messages the class unguarded. Older clang emitted a warning for messaging a forward-declared class; the current CLT promotes it to a hard error. So macOS builds work until the developer updates Command Line Tools, then break.

Fix

Upstream SDL fixed this on the SDL2 maintenance line in libsdl-org/SDL@0b6eff41 ("Fixed building on macOS with OpenGL disabled"), first shipped in 2.32.0; the 2.30.x branch never received the backport. Bumping the builder's checkout to a 2.32.x tag fixes it, e.g.:

cmd_ = [
    'cd lib/SDL && git checkout release-2.32.8 2>/dev/null '
    '|| (git fetch --tags && git checkout release-2.32.8)'
]

(The fetch fallback covers existing clones that predate the tag.)

Verified on macOS with the 26.5 SDK: 2.30.2 fails with the error above; 2.32.8 compiles cleanly and the resulting binary runs normally. Happy to open a PR if useful.

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