[dexter1]

SPROC and pthreads cannot coexist in one program, they are mutually exclusive.
If lscs_mp requires SPROC then your code should use SPROC only.

I understand that the code you're using is using pthreads, this means that you need to use something else to solve large sparse matrices.
Because i have worked in numerical engineering for quite some time, may i suggest to you libraries like UMFPACK or SPQR?
These are well suited for solving large sparse matrices with respectively full rank or rank deficient systems.
See http://faculty.cse.tamu.edu/davis/suitesparse.html for code. You may need an older version for SPQR to compile it under IRIX systems

They require fast BLAS and LAPACK libraries, these are provided in IRIX, or you could roll-your-own using ATLAS, see http://math-atlas.sourceforge.net/