ddrutility: add -fcommon workaround

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

    ld: /build/ccltHly5.o:(.bss+0x119f8): multiple definition of `start_time'; /build/cc9evx3L.o:(.bss+0x10978): first defined here

pkgs/tools/system/ddrutility/default.nix

@@ -13,6 +13,11 @@ stdenv.mkDerivation rec {
     substituteInPlace makefile --replace /usr/local ""
   '';
 
+  # Workaround build failure on -fno-common toolchains like upstream
+  # gcc-10. Otherwise build fails as:
+  #   ld: /build/ccltHly5.o:(.bss+0x119f8): multiple definition of `start_time'; /build/cc9evx3L.o:(.bss+0x10978): first defined here
+  NIX_CFLAGS_COMPILE = "-fcommon";
+
   makeFlags = [ "DESTDIR=$(out)" ];
 
   meta = with lib; {