[gcc] Fix addsi patterns for nacl64 PIC

This is similar to a bunch of previous fixes: prevent define_expands and define_insns from treating ILP32 PIC symbol_ref as an immediate.

BUG=http://code.google.com/p/nativeclient/issues/detail?id=872

TEST=

Review URL: http://codereview.chromium.org/3291022
1 file changed