gn2bp: Fix arch-dependent cc_genrule

* The cmd of the `cc_genrule` is now arch-dependent. So we no longer generate a genrule for each arch.
  The propagation of the arch-dependent genrule was broken due to an old if-statement.

Test: m
Change-Id: I4b9b522c429f32fe74d141b00bd856f6c39498d7
1 file changed