Working meep installation

[ddeeptimahanti]

Fails to pick lfftw during link stage

     158    checking dynamic linker characteristics... (cached) GNU/Linux ld.so
     159    checking how to hardcode library paths into programs... immediate
     160    checking how to get verbose linking output from /software/setonix/2023.08/spack/lib/spack/env/gcc/gfortran... -v
     161    checking for Fortran 77 libraries of /software/setonix/2023.08/spack/lib/spack/env/gcc/gfortran...  -L/opt/cray/pe/mpich/8.1.25/ofi/gnu/9.1/lib -L/opt/cray/pe/
            libsci/23.02.1.1/GNU/9.1/x86_64/lib -L/opt/cray/pe/dsmml/0.2.2/dsmml//lib -L/opt/cray/xpmem/2.5.2-2.4_3.47__gd0f7936.shasta/lib64 -L/opt/cray/pe/gcc/12.2.0/sno
            s/lib/gcc/x86_64-suse-linux/12.2.0 -L/opt/cray/pe/gcc/12.2.0/snos/lib/gcc/x86_64-suse-linux/12.2.0/../../../../lib64 -L/lib/../lib64 -L/usr/lib/../lib64 -L/sof
            tware/setonix/2023.08/software/linux-sles15-zen3/gcc-12.2.0/python-3.10.10-bk4mjnuv6ufkvy3gb5h62l65dgv6zost/lib -L/opt/cray/pe/gcc/12.2.0/snos/lib/gcc/x86_64-s
            use-linux/12.2.0/../../.. -lfftw3 -lgfortran -lm -lmpifort_gnu_91 -lmpi_gnu_91 -lxpmem -lsci_gnu_82_mpi -lsci_gnu_82 -ldl -ldsmml -lquadmath -lpthread -lfftw3:
     162    checking for dummy main to link with Fortran 77 libraries... unknown
  >> 163    configure: error: in `/scratch/pawsey0001/ddeeptimahanti/setonix/2023.08/software/ddeeptimahanti/build_stage/spack-stage-meep-1.25.0-swgm7lfqf7a7xkmg6bcscmqbu4
            y4znhp/spack-src':
  >> 164    configure: error: linking to Fortran libraries from C fails

Key to resolve this issue is this function:

    def setup_build_environment(self, env):
        env.append_flags("LDFLAGS", self.spec["fftw"].libs.search_flags)

[ddeeptimahanti]

@pelahi and @ilkhomab - only one group is using this package so not worth going into this repository. So, I'll close this PR.