Fix nanos6 cross-compilation for riscv

pkgs/nanos6/default.nix

@@ -78,6 +78,8 @@ in
     ] ++
       (optional enableJemalloc "--with-jemalloc=${jemallocNanos6}") ++
       (optional enableGlibcxxDebug "CXXFLAGS=-D_GLIBCXX_DEBUG") ++
+      # Most nanos6 api symbols are resolved at runtime, so prefer
+      # ifunc by default
       (optional isCross "--with-symbol-resolution=ifunc");
 
     postConfigure = lib.optionalString (!enableDebug) ''