(in minc-toolkit-v2 superbuild) if external openblas is used, libgfortran is not included in linking

[gdevenyi]

Probably related to #4, after fixing it, I get this new error:

[ 13%] Linking CXX executable itk_patch_grading
/scinet/niagara/software/2018a/opt/base/openblas/0.2.20/lib/libopenblas.a(dormlq.o): In function `dormlq_':
dormlq.f:(.text+0x326): undefined reference to `_gfortran_concat_string'
dormlq.f:(.text+0x7b1): undefined reference to `_gfortran_concat_string'
/scinet/niagara/software/2018a/opt/base/openblas/0.2.20/lib/libopenblas.a(dormqr.o): In function `dormqr_':
dormqr.f:(.text+0x330): undefined reference to `_gfortran_concat_string'
dormqr.f:(.text+0x793): undefined reference to `_gfortran_concat_string'
/scinet/niagara/software/2018a/opt/base/openblas/0.2.20/lib/libopenblas.a(iparam2stage.o): In function `iparam2stage_':
iparam2stage.F:(.text+0x1c9): undefined reference to `_gfortran_compare_string'
make[2]: *** [src/itk_patch_grading] Error 1
make[1]: *** [src/CMakeFiles/itk_patch_grading.dir/all] Error 2
make: *** [all] Error 2

(also happens for itk_patch_grading)

This I fixed by (wrongly) editing the link.txt for each to add "-lgfortran" to the linking call.

I suspect the root cause of this might be the same as #4