[PowerPC][AIX] Fallback to DAG-ISEL if global has toc-data attribute.

FAST-ISEL should fall back to DAG-ISEL when a global variable has the
toc-data attribute. A number of the checks were duplicated in the lit
test becuase of
1) Slightly different output between -O0 and -O2 due to FAST-ISEL vs
   DAG-ISEL codegen.
2) In preperation of a peephole optimization that will run when
   optimizations are enabled.

Differential Revision: https://reviews.llvm.org/D115373