Changes to the Clang packaging script:
 - package the iOS simulator ASan runtime and set the correct LC_ID_DYLIB for it
 - declare gcc_toolchain to fix the "unbound variable" errors

BUG=170629,344836
R=thakis@chromium.org

Review URL: https://codereview.chromium.org/170873008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252561 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 252561