Performance optimization for NEC SX AURORA (!97)

The subroutines `init_zero_4d_[dp,sp,i4]` do not vectorize properly on NEC SX AURORA.

Loop collapsing is enforced by a compiler directive for the subroutines `init_zero_4d_[dp,sp,i4]`, in order to ensure proper vectorization on NEC SX AURORA.

Approved-by: Yen-Chen Chen <yen-chen.chen@kit.edu>
Merged-by: Yen-Chen Chen <yen-chen.chen@kit.edu>
Changelog: feature

src/mo_fortran_tools.F90

@@ -1201,6 +1201,7 @@ CONTAINS
 #else
 !$omp do collapse(4)
 #endif
+!NEC$ forced_collapse
     DO i4 = 1, m4
       DO i3 = 1, m3
         DO i2 = 1, m2
@@ -1235,6 +1236,7 @@ CONTAINS
 #else
 !$omp do collapse(4)
 #endif
+!NEC$ forced_collapse
     DO i4 = 1, m4
       DO i3 = 1, m3
         DO i2 = 1, m2
@@ -1269,6 +1271,7 @@ CONTAINS
 #else
 !$omp do collapse(4)
 #endif
+!NEC$ forced_collapse
     DO i4 = 1, m4
       DO i3 = 1, m3
         DO i2 = 1, m2