Support configuration with optional BLAS or Eigen3, and disabling FC completely

Move some Fortran language checkers inside if checks so that disable fortran works correctly. There is still a name mangling check before BLAS that is unclear how to get rid off

Adding configure options to --disable-blaslapack (only with Eigen3 is enabled), and a way to provide --with-fc-mangling-suffix="_" so that we dont need a fortran compiler to introspect.

Fix a compiler error due to a previous commented out configure command