ninja&make/mac: Only pass -x to strip for loadable_modules.

I misinterpreted what "Bundle products" meant in the "Default value" row
for STRIP_STYLE on
https://developer.apple.com/library/mac/documentation/DeveloperTools/Reference/XcodeBuildSettingRef/1-Build_Setting_Reference/build_setting_ref.html#//apple_ref/doc/uid/TP40003931-CH3-SW153

BUG=280718
R=mark@chromium.org

Review URL: https://codereview.chromium.org/23600042

git-svn-id: http://gyp.googlecode.com/svn/trunk@1730 78cadc50-ecff-11dd-a971-7dbc132099af