freebayes: add -fcommon workaround

Workaround build failure on -fno-common toolchains like upstream
gcc-10. Otherwise build fails as:

    ld: foomatic_rip-options.o:/build/foomatic-filters-4.0.17/options.c:49: multiple definition of `cupsfilter';
      foomatic_rip-foomaticrip.o:/build/foomatic-filters-4.0.17/foomaticrip.c:158: first defined here

pkgs/applications/science/biology/freebayes/default.nix

@@ -15,6 +15,12 @@ stdenv.mkDerivation rec {
 
   buildInputs = [ zlib bzip2 xz ];
 
+  # Workaround build failure on -fno-common toolchains like upstream
+  # gcc-10. Otherwise build fails as:
+  #   ld: foomatic_rip-options.o:/build/foomatic-filters-4.0.17/options.c:49: multiple definition of `cupsfilter';
+  #     foomatic_rip-foomaticrip.o:/build/foomatic-filters-4.0.17/foomaticrip.c:158: first defined here
+  NIX_CFLAGS_COMPILE = "-fcommon";
+
   installPhase = ''
     install -vD bin/freebayes bin/bamleftalign scripts/* -t $out/bin
   '';