STYLE: add sub-directories in OSspecific/POSIX

src/OSspecific/POSIX/Make/files

+POSIX.C
+
 cpuInfo/cpuInfo.C
 cpuTime/cpuTimePosix.C
 memInfo/memInfo.C
@@ -10,20 +12,19 @@ signals/sigStopAtWriteNow.C
 signals/sigWriteNow.C
 signals/timer.C
 
-regExpPosix.C
-fileStat.C
-POSIX.C
+regExp/regExpPosix.C
+fileStat/fileStat.C
 
 /*
- * Note: fileMonitor assumes inotify by default. Compile with -DFOAM_USE_STAT
- * to use stat (=timestamps) instead of inotify
+ * fileMonitor assumes inotify by default.
+ * Compile with -UFOAM_USE_INOTIFY to use stat (timestamps) instead
  */
-fileMonitor.C
+fileMonitor/fileMonitor.C
 
 #ifdef __sun__
-dummyPrintStack.C
+printStack/dummyPrintStack.C
 #else
-printStack.C
+printStack/printStack.C
 #endif
 
 LIB = $(FOAM_LIBBIN)/libOSspecific