rts/PrimOps.cmm: follow '_static_closure' update

Caught by UNREG build failure:

      rts_dist_HC rts/dist/build/PrimOps.o
    /tmp/ghc8613_0/ghc8613_2.hc: In function 'cf8_entry':

    /tmp/ghc8613_0/ghc8613_2.hc:1942:13:
         error: 'base_ControlziExceptionziBase_nestedAtomically_static_closure' undeclared (first use in this function)
         R1.w = (W_)&base_ControlziExceptionziBase_nestedAtomically_static_closure;
                     ^

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>