Loki: enable imports and mark headers as ignored instead of blocked

[reuterbal]

This is an alternative solution to #79.

• re-enables chasing import dependencies (after the last-minute default behaviour change in Loki)
• fixes the problem that the header module defining NCLV, which is required for variable demotion, was marked as blocked and not ignored

Performance looks good with this, and demotion verified by diff'ing against the gpu_scc variant:

$ NV_ACC_CUDA_HEAPSIZE=6G bin/dwarf-cloudsc-loki-scc 1 163840 128
     NUMPROC=1, NUMOMP=1, NGPTOTG=163840, NPROMA=128, NGPBLKS=1280
 Reference MFLOP count for 100 columns :  12.48232900
     NUMOMP    NGPTOT  #GP-cols     #BLKS    NPROMA tid# : Time(msec)  MFlops/s     col/s
          1    163840    163840         1       128    0 :        105    194538   1558509 @ rank#0:core#172
          1    163840    163840      1280       128   -1 :       1613     12671    101518 : TOTAL @ rank#0
    1 x   1    163840    163840      1280       128   -1 :       1613     12671    101518 : TOTAL
...
$ bin/dwarf-cloudsc-loki-scc-hoist 1 163840 128
     NUMPROC=1, NUMOMP=1, NGPTOTG=163840, NPROMA=128, NGPBLKS=1280
 Reference MFLOP count for 100 columns :  12.48232900
     NUMOMP    NGPTOT  #GP-cols     #BLKS    NPROMA tid# : Time(msec)  MFlops/s     col/s
          1    163840    163840         1       128    0 :         62    329376   2638741 @ rank#0:core#172
          1    163840    163840      1280       128   -1 :       1573     12998    104134 : TOTAL @ rank#0
    1 x   1    163840    163840      1280       128   -1 :       1573     12998    104134 : TOTAL
...
$ bin/dwarf-cloudsc-loki-scc-stack 1 163840 128
     NUMPROC=1, NUMOMP=1, NGPTOTG=163840, NPROMA=128, NGPBLKS=1280
 Reference MFLOP count for 100 columns :  12.48232900
     NUMOMP    NGPTOT  #GP-cols     #BLKS    NPROMA tid# : Time(msec)  MFlops/s     col/s
          1    163840    163840         1       128    0 :         62    325949   2611287 @ rank#0:core#38
          1    163840    163840      1280       128   -1 :       1561     13096    104920 : TOTAL @ rank#0
    1 x   1    163840    163840      1280       128   -1 :       1561     13096    104920 : TOTAL

[mlange05]

Looks great and works as intended. Many thanks for tracking this down. GTG from me 🚢