CMake: properly check for Haiku headers

CMakeLists.txt

@@ -729,11 +729,23 @@ endif ( enable-readline )
 unset ( HAIKU_SUPPORT CACHE )
 unset ( MIDIKIT2_SUPPORT CACHE )
 if ( enable-haiku )
-  set ( HAIKU_SUPPORT 1 )
+  check_include_file_cxx("MediaKit.h" HAVE_MEDIAKIT_H)
+  check_include_file_cxx("SupportKit.h" HAVE_SUPPORTKIT_H)
+  if ( HAVE_MEDIAKIT_H AND HAVE_SUPPORTKIT_H )
+    set ( HAIKU_SUPPORT TRUE )
+  else ( HAVE_MEDIAKIT_H AND HAVE_SUPPORTKIT_H )
+    set ( HAIKU_SUPPORT FALSE )
+  endif ( HAVE_MEDIAKIT_H AND HAVE_SUPPORTKIT_H )
 endif ( enable-haiku )
 
 if ( enable-midikit2 )
-  set ( MIDIKIT2_SUPPORT 1 )
+  check_include_file_cxx("Midi2Defs.h" HAVE_MIDI2DEFS_H)
+  check_include_file_cxx("MidiRoster.h" HAVE_MIDIROSTER_H)
+  if ( HAVE_MIDI2DEFS_H AND HAVE_MIDIROSTER_H )
+    set ( MIDIKIT2_SUPPORT TRUE )
+  else ( HAVE_MIDI2DEFS_H AND HAVE_MIDIROSTER_H )
+    set ( MIDIKIT2_SUPPORT FALSE )
+  endif ( HAVE_MIDI2DEFS_H AND HAVE_MIDIROSTER_H )
 endif ( enable-midikit2 )
 
 unset ( AUFILE_SUPPORT CACHE )