libipfix: add -fcommon workaround

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

    ld: ../libmisc/libmisc.a(mlog.o):/build/libipfix_110209/libmisc/misc.h:111: multiple definition of
      `ht_globals'; collector.o:/build/libipfix_110209/collector/../libmisc/misc.h:111: first defined here

pkgs/development/libraries/libipfix/default.nix

@@ -7,6 +7,14 @@ stdenv.mkDerivation {
     url = "mirror://sourceforge/libipfix/files/libipfix/libipfix_110209.tgz";
     sha256 = "0h7v0sxjjdc41hl5vq2x0yhyn04bczl11bqm97825mivrvfymhn6";
   };
+
+  # Workaround build failure on -fno-common toolchains:
+  #   ld: ../libmisc/libmisc.a(mlog.o):/build/libipfix_110209/libmisc/misc.h:111: multiple definition of
+  #     `ht_globals'; collector.o:/build/libipfix_110209/collector/../libmisc/misc.h:111: first defined here
+  # TODO: drop the workaround when fix ix released:
+  #   https://sourceforge.net/p/libipfix/code/ci/a501612c6b8ac6f2df16b366f7a92211382bae6b/
+  NIX_CFLAGS_COMPILE = "-fcommon";
+
   meta = with lib; {
     homepage = "http://libipfix.sourceforge.net/";
     description = "The libipfix C-library implements the IPFIX protocol defined by the IP Flow Information Export working group of the IETF";