Fix build on current GNUstep and CALayer struct-property KVO crash

[pkgdemon]

Summary

Two related changes so libs-quartzcore builds and the bundled demo
actually runs on current GNUstep/Linux:

1. Build fixes so the headers and sources compile against the
   current generation of GNUstep core (Foundation/CoreFoundation) and
   against a non-Apple OpenGL.
2. CALayer KVO fix: struct-typed animatable properties
   (bounds, position, anchorPoint, transform, sublayerTransform,
   contentsRect, shadowOffset) can no longer be registered for
   automatic KVO observation on GNUstep — the autogenerated setter
   overrides corrupt struct arguments passed by value through
   objc_msgSend. The demo app crashed on startup before this.

Build changes (da7275a)

• Headers/QuartzCore/CABase.h — import Foundation/NSObject.h before
  CoreFoundation.h so CF inline functions can resolve -hash /
  -isEqual: signatures. (Same pattern libs-opal needs on current
  GNUstep.)
• Headers/QuartzCore/CATransaction.h — switch from
  #import "CoreFoundation/CFDate.h" to
  #import <CoreFoundation/CoreFoundation.h>. The quoted per-header
  path doesn't resolve reliably against libs-corebase install layout.
• Source/CABackingStore.h — move #define GL_GLEXT_PROTOTYPES 1
  outside the Apple-only block so non-Apple builds also get it, and
  add #import <GL/glext.h> for the non-Apple path.
• Source/GNUmakefile / config.make — minor flag adjustments for
  the current toolchain.
• .gitignore — ignore obj/, derived_src/, *.framework/,
  *.app/.

CALayer fix (2ae02bb)

CALayer -init used to register every property in its defaults list
for KVO observation via CAImplicitAnimationObserver. On GNUstep this
works for object-typed properties but breaks for struct-typed ones:
the KVO machinery generates a setter override that receives the struct
by value through objc_msgSend, and on GNUstep the argument marshalling
corrupts the struct contents. Setting bounds/position/etc. on a
fresh layer would then either crash or write garbage.

Changes in Source/CALayer.m:

• Maintain a separate structKeys list: anchorPoint, transform,
  sublayerTransform, contentsRect, shadowOffset, bounds,
  position. These are excluded from addObserver:forKeyPath:.
  Their setters already emit willChange/didChange via
  GSCA_OBSERVABLE_SETTER / the manual -setBounds: / -setPosition:,
  so implicit animations still fire.
• Add default-value handling for transform and sublayerTransform
  analogous to the existing shadowOffset special-case: try KVC first,
  fall back to the typed setter inside NS_DURING / NS_HANDLER.
• Wrap the remaining (non-struct) addObserver: in NS_DURING / NS_HANDLER
  so property types that don't support automatic KVO (e.g. CGColorRef)
  don't abort -init.
• Drop a dead #if 0 debug block.

Demo changes (2ae02bb)

• Demo/AppController.m — remove the hand-rolled NSMenu creation
  under #if GNUSTEP. The main menu is already provided through the
  standard GNUstep app loading path; the duplicate menu setup was a
  leftover.
• Rename GSQuartzCoreDemo → QuartzCoreDemo in the Info.plist
  (ApplicationName, NSExecutable) to match the current bundle name.
• Trailing whitespace fix in DemoOpenGLView.m.

Compatibility

• macOS/Apple build path: unchanged; all CALayer.m changes are
  additive to the existing Apple code paths.
• GNUstep with libs-corebase installed: header includes resolve
  through <CoreFoundation/CoreFoundation.h> as expected.

Testing

• Built cleanly against current GNUstep core (libs-base, libs-gui,
  libs-corebase, libs-opal) on Devuan/Linux x86_64.
• The bundled Demo/ QuartzCore demo launches, the CALayer tree is
  created without crashing, and the root layer renders through the
  GL view.

[pkgdemon]

Note this depends on gnustep/libs-opal#16

[pkgdemon]

@gcasa Here are fixes discussed in last GNUstep meeting.

[pkgdemon]

@ivucica Let me know if this is something you might want, or if you foresee the need for a lot of changes. I did get libs-opal fixes merged so this will build now.

[pkgdemon]

@ivucica Also something else from the readme I am not sure this is the case anymore:

Patched Opal. Opal currently conflicts with AppKit. More specifically, it also implements an incompatible NSFont. An experimental patch is provided against r35173 of Opal in opal-nsfonthacks.patch.
Opal requires Cairo and may require corebase.

At least with my PR the demo app works fine, and no other patches required.