While libmtsk is used by code generated for OpenMP, it is also used for other forms of parallel programming. The array libraries call routines in libmtsk to implement parallel versions of array operations.
The library libmtsk ships as part of Solaris. Any version of Solaris capable of running Oracle Solaris Studio 12.4 should include a copy of libmtsk that has the required version set. Do you know the date or update level of release of Solaris 10 you are running?
You could try to link your program without including the array libraries on the link line. You can see the link line generated by the compiler driver by using the option -v.
Bob Corbett