[BasicAA] Add test showing 32 bit overflow issue for GEPs.

This patch additional tests with i64 GEP indices for 32 bit pointers.
@mustalias_overflow_in_32_bit_add_mul_gep highlights a case where
BasicAA currently incorrectly determines noalias.

Modeled in Alive2 for 32 bit pointers: https://alive2.llvm.org/ce/z/HHjQgb
Modeled in Alive2 for 64 bit pointers: https://alive2.llvm.org/ce/z/DoWK2c