Xcode configuration woe

[Vincent Habchi]

Folks,

I try to update QGis to 3.4.1, and stumble on that compilation error:

—
/opt/local/var/macports/build/_macports-ports_gis_qgis3/qgis3/work/QGIS-3_4_1/src/native/mac/qgsmacnative.mm:125:18: error: property 'effectiveAppearance' not found on object of type '__kindof NSApplication *'
  return ( NSApp.effectiveAppearance.name == NSAppearanceNameDarkAqua );
                 ^
/opt/local/var/macports/build/_macports-ports_gis_qgis3/qgis3/work/QGIS-3_4_1/src/native/mac/qgsmacnative.mm:125:46: error: use of undeclared identifier 'NSAppearanceNameDarkAqua'; did you mean 'NSAppearanceNameAqua'?
  return ( NSApp.effectiveAppearance.name == NSAppearanceNameDarkAqua );
                                             ^~~~~~~~~~~~~~~~~~~~~~~~
                                             NSAppearanceNameAqua
/System/Library/Frameworks/AppKit.framework/Headers/NSAppearance.h:56:38: note: 'NSAppearanceNameAqua' declared here
APPKIT_EXTERN NSAppearanceName const NSAppearanceNameAqua NS_AVAILABLE_MAC(10_9);
                                     ^
—
Alright, when I look at the file /System/Library/Frameworks/AppKit.framework/Headers/NSAppearance.h, I get:

-rw-r--r--  1 root  wheel  2699 15 Mar  2018 /System/Library/Frameworks/AppKit.framework/Headers/NSAppearance.h

Which means that file is one release behind (10.13 instead of 10.14). However

-rw-r--r--  1 root  wheel  3721 16 Oct 07:20 /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks/AppKit.framework/Headers/NSAppearance.h

Is correct. Question: how to make clang use that header instead of the one installed in /System? Also, did I miss something?

Thanks,
Vincent