Fix typo cflags->ldflags in nss BUILD.gn on mac

The gyp file has this in OTHER_LDFLAGS.

TBR=brettw@chromium.org

Review URL: https://codereview.chromium.org/308003010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@274123 0039d316-1c4b-4281-b951-d872f2087c98

tools/gn/secondary/third_party/nss/BUILD.gn

@@ -356,7 +356,7 @@ if (is_linux) {
 
     if (component_mode == "shared_library") {
       if (is_mac) {
-        cflags = [ "-all_load" ]
+        ldflags = [ "-all_load" ]
       } else if (is_win) {
         # Pass the def file to the linker.
         ldflags = [ rebase_path("nss/exports_win.def", root_build_dir) ]