Find{BLAS,LAPACK}: Fix MKL with gfortran
- In FindBLAS: the gf interface and gnu threading libraries (and the corresponding omp lib) are searched for instead of the intel ones when GNU compilers are used. Some other minor fixes.
- In FindLAPACK: the vendors search order now matches the one in FindBLAS. Some other minor fixes and cleaning
Fixes: #18561 (closed)