buildGoModule: add ./ to all sub-packages (#63936)

When $subPackages has more than one item, the build was failing because
./ was added only to the first subPackage. This commit adds ./ to all
specified subPackages.

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

@@ -125,7 +125,7 @@ let
         local type;
         type="$1"
         if [ -n "$subPackages" ]; then
-          echo "./$subPackages"
+          echo "$subPackages" | sed "s,\(^\| \),\1./,g"
         else
           find . -type f -name \*$type.go -exec dirname {} \; | grep -v "/vendor/" | sort --unique
         fi
@@ -144,6 +144,7 @@ let
           export NIX_BUILD_CORES=1
       fi
       for pkg in $(getGoDirs ""); do
+        echo "Building subPackage $pkg"
         buildGoDir install "$pkg"
       done
     '' + lib.optionalString (stdenv.hostPlatform != stdenv.buildPlatform) ''