fltk: fix on darwin

Compiling Fl_cocoa.mm...
Fl_cocoa.mm:4079:30: error: use of undeclared identifier 'version'; did
you mean 'Fl::version'?
NSOperatingSystemVersion version = [[NSProcessInfo processInfo]
operatingSystemVersion];
^~~~~~~
Fl::version
../FL/Fl.H:262:17: note: 'Fl::version' declared here
static double version();
^
Fl_cocoa.mm:4079:5: error: use of undeclared identifier
'NSOperatingSystemVersion'
NSOperatingSystemVersion version = [[NSProcessInfo processInfo]
operatingSystemVersion];
^
Fl_cocoa.mm:4080:9: error: use of undeclared identifier 'version'
M = version.majorVersion;
^
Fl_cocoa.mm:4081:9: error: use of undeclared identifier 'version'
m = version.minorVersion;
^
Fl_cocoa.mm:4082:9: error: use of undeclared identifier 'version'
b = version.patchVersion;
^
5 errors generated.

pkgs/development/libraries/fltk/default.nix

···
       --replace 'class Fl_XFont_On_Demand' 'class FL_EXPORT Fl_XFont_On_Demand'
   '';
 
+  patches = stdenv.lib.optionals stdenv.isDarwin [ ./nsosv.patch ];
+
   nativeBuildInputs = [ pkgconfig ];
   propagatedBuildInputs = [ inputproto ]
     ++ (if stdenv.isDarwin

pkgs/development/libraries/fltk/nsosv.patch

···
+diff --git a/src/Fl_cocoa.mm b/src/Fl_cocoa.mm
+index 6f5b8b1..2c7763d 100644
+--- a/src/Fl_cocoa.mm
++++ b/src/Fl_cocoa.mm
+@@ -4074,15 +4074,6 @@ Window fl_xid(const Fl_Window* w)
+ static int calc_mac_os_version() {
+   int M, m, b = 0;
+   NSAutoreleasePool *localPool = [[NSAutoreleasePool alloc] init];
+-#if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_10
+-  if ([NSProcessInfo instancesRespondToSelector:@selector(operatingSystemVersion)]) {
+-    NSOperatingSystemVersion version = [[NSProcessInfo processInfo] operatingSystemVersion];
+-    M = version.majorVersion;
+-    m = version.minorVersion;
+-    b = version.patchVersion;
+-  }
+-  else
+-#endif
+   {
+     NSDictionary * sv = [NSDictionary dictionaryWithContentsOfFile:@"/System/Library/CoreServices/SystemVersion.plist"];
+     const char *s = [[sv objectForKey:@"ProductVersion"] UTF8String];