Fix "line 2: BUILT_PRODUCTS_DIR: command not found". <(PRODUCT_DIR) expands

to an Xcode variable, $(BUILT_PRODUCTS_DIR), which is not a shell variable.
The shell tries to treat it as a command expansion.  Use ${BUILT_PRODUCTS_DIR}
directly.

BUG=none
TEST=Nico
Review URL: http://codereview.chromium.org/353002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@30686 0039d316-1c4b-4281-b951-d872f2087c98