buildGoModule: share the buildFlagsArray with the parallel subprocesses

pkgs/development/go-modules/generic/default.nix

@@ -116,6 +116,7 @@ go.stdenv.mkDerivation (
       local d; local cmd;
       cmd="$1"
       d="$2"
+      . $TMPDIR/buildFlagsArray
       echo "$d" | grep -q "\(/_\|examples\|Godeps\)" && return 0
       [ -n "$excludedPackages" ] && echo "$d" | grep -q "$excludedPackages" && return 0
       local OUT
@@ -143,6 +144,11 @@ go.stdenv.mkDerivation (
       fi
     }
 
+    if [ ''${#buildFlagsArray[@]} -ne 0 ]; then
+      declare -p buildFlagsArray > $TMPDIR/buildFlagsArray
+    else
+      touch $TMPDIR/buildFlagsArray
+    fi
     export -f buildGoDir # parallel needs to see the function
     if [ -z "$enableParallelBuilding" ]; then
         export NIX_BUILD_CORES=1