return OS/2 support to avoid binary incompatibility

This partially reverts commit d7bc3048ee87ca5cb190fe8236b354db9b9ef39e
"Remove OS/2 support."

offapi/com/sun/star/setup/OSType.idl

@@ -42,6 +42,9 @@ published enum OSType
     // DocMerge: empty anyway
     WIN,
 
+    // DocMerge: empty anyway
+    OS2,
+
     // DocMerge: empty anyway
     MAC,
 

udkapi/com/sun/star/lang/SystemDependent.idl

@@ -94,6 +94,11 @@ published constants SystemDependent
 
     //-------------------------------------------------------------------------
 
+    // DocMerge from idl: value com::sun::star::lang::SystemDependent::SYSTEM_OS2
+    /** The called interface method returns a value specified for the <em>OS/2</em> system.
+     */
+    const short SYSTEM_OS2 = 4;
+
     // DocMerge from idl: value com::sun::star::lang::SystemDependent::SYSTEM_MAC
     /** The called interface method returns a value specified for the <em>MAC-OS</em> system.
      */