osaThread: added missing include for Ubuntu 24.04

Author: adeguet1

cisstOSAbstraction/osaThread.h

@@ -39,7 +39,8 @@ no warranty.  The complete license can be found in license.txt and
 #define SCHED_FIFO 0   /*! No Scheduling Policy available in Windows */
 #endif
 
-#if (CISST_OS == CISST_DARWIN) // SCHED_FIFO is not defined otherwise
+// SCHED_FIFO is not defined otherwise
+#if (CISST_OS == CISST_LINUX) || (CISST_OS == CISST_DARWIN)
 #include <pthread.h>
 #endif