workaround for kCTForegroundColorFromContextAttributeName unavailability

fixes "error: ‘kCTForegroundColorFromContextAttributeName’ was not declared in this scope"

see commits:
  5bc53876

Change-Id: Ifdf69ab2f9a6437d18a6d3e3f5d756beeed3ba5c
Reviewed-on: https://gerrit.libreoffice.org/9758Reviewed-by: Noel Grandin <noelgrandin@gmail.com>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

vcl/quartz/ctfonts.cxx

@@ -27,6 +27,10 @@
 #ifdef MACOSX
 #include "osx/salinst.h"
 #include "osx/saldata.hxx"
+// kCTForegroundColorFromContextAttributeName is available on 10.5, but it is "hidden"
+#ifndef kCTForegroundColorFromContextAttributeName
+extern const CFStringRef kCTForegroundColorFromContextAttributeName;
+#endif
 #endif
 #include "quartz/salgdi.h"
 #include "quartz/utils.h"
@@ -103,7 +107,6 @@ CoreTextStyle::CoreTextStyle( const FontSelectPattern& rFSD )
     // allow delayed setting the font color, i.e. after the text layout
     CFDictionarySetValue( mpStyleDict, kCTForegroundColorFromContextAttributeName, kCFBooleanTrue );
 
-
 #if 0 // LastResort is implicit in CoreText's font cascading
     const void* aGFBDescriptors[] = { CTFontDescriptorCreateWithNameAndSize( CFSTR("LastResort"), 0) }; // TODO: use the full GFB list
     const int nGfbCount = sizeof(aGFBDescriptors) / sizeof(*aGFBDescriptors);