fftw: add fftwLongDouble, disable SSE2 in that case

pkgs/development/libraries/fftw/default.nix

···
     ]
     ++ optional (precision != "double") "--enable-${precision}"
     # all x86_64 have sse2
-    ++ optional stdenv.isx86_64 "--enable-sse2"
+    # however, not all float sizes fit
+    ++ optional (stdenv.isx86_64 && (precision == "single" || precision == "double") )  "--enable-sse2"
     ++ optional stdenv.cc.isGNU "--enable-openmp";
 
   enableParallelBuilding = true;

pkgs/top-level/all-packages.nix

···
   fftw = callPackage ../development/libraries/fftw { };
   fftwSinglePrec = fftw.override { precision = "single"; };
   fftwFloat = fftwSinglePrec; # the configure option is just an alias
+  fftwLongDouble = fftw.override { precision = "long-double"; };
 
   filter-audio = callPackage ../development/libraries/filter-audio {};