FindLAPACK: Add '-fortranlibs' flag only with NVHPC/PGI compilers

Since commit 2c9e623e31 (Find{BLAS,LAPACK}: Add support for the NVHPC
LAPACK library, 2021-05-05, v3.21.0-rc1~192^2) we try the `-fortranlibs`
option as a dependency of the NVHPC LAPACK.  That flag is specific to
the NVHPC/PGI compilers, so use it conditionally with them.

Without this modification, CMake fails to find LAPACK if

- compiler ID is GNU
- `BLA_STATIC` is `ON`
- `BLA_VENDOR` is not defined or set to `All`

Fixes: #23705, #22878