Revert "Remove OpenMP pragmas from TMatrix multiplication function"

This reverts commit 10b6c35.

Author: guitargeek

math/matrix/src/TMatrixT.cxx

@@ -3096,6 +3096,9 @@ void TMatrixTAutoloadOps::AMultB(const Element *const ap, Int_t na, Int_t ncolsa
       return;
    }
    const Int_t BLOCK = (M >= 192 && N >= 192 && P >= 192) ? 48 : 32;
+#ifdef _OPENMP
+#pragma omp parallel for collapse(2) if (M * P > 10000)
+#endif
    for (Int_t i0 = 0; i0 < M; i0 += BLOCK) {
       for (Int_t j0 = 0; j0 < P; j0 += BLOCK) {
          const Int_t i1 = (i0 + BLOCK < M) ? i0 + BLOCK : M;