[Lazarus] patch for rx.inc define linux_darwin definition

[FreeMan]

I added patch for rx using in osx
this is just add "Linux_Darwin" compiler directive in rx.inc file.
If you want use this, You have to change "Linux_Darwin" with {$...... 
LINUX} I mean, change "LINUX" to "Linux_Darwin". original rx code just 
use compiler directive if linux .... else ...    else for windows
TRxDBLookupCombo when click button, grind create on behind form and can 
not access it.
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Index: rx.inc
===================================================================
--- rx.inc	(revision 3968)
+++ rx.inc	(working copy)
@@ -58,3 +58,12 @@
 {$ENDIF}
 
 {.$DEFINE RxDBGridDepricatedProps}
+//freeman added
+{$IFDEF DARWIN}
+  {$DEFINE Linux_Darwin}
+{$ENDIF DARWIN}
+
+{$IFDEF LINUX}
+  {$DEFINE Linux_Darwin}
+{$ENDIF LINUX}
+