Fix: print namespace variable names, too.

Bug: 193540681
Test: internal
Change-Id: I1827411e7c6e693666e40fcbcad34ff7bc82ef20
diff --git a/core/product_config.rbc b/core/product_config.rbc
index 8fbcfa5..28b37a3 100644
--- a/core/product_config.rbc
+++ b/core/product_config.rbc
@@ -82,7 +82,7 @@
                     # Define SOONG_CONFIG_<ns> for Make, othewise
                     # it cannot be added to .KATI_READONLY list
                     if _options.format == "make":
-                        print("SOONG_CONFIG_" + nsname, ":=")
+                        print("SOONG_CONFIG_" + nsname, ":=", " ".join(nsvars.keys()))
                     for var, val in sorted(nsvars.items()):
                         __print_attr("SOONG_CONFIG_%s_%s" % (nsname, var), val)
             elif attr not in _globals_base: