BPF: support inlining __builtin_memcmp intrinsic call

Delyan Kratunov reported an issue where __builtin_memcmp is
not inlined into simple load/compare instructions.
This is a known issue. In the current state, __builtin_memcmp
will be converted to memcmp call which won't work for
bpf programs.

This patch added support for expanding __builtin_memcmp with
actual loads and compares up to currently maximum 128 total loads.
The implementation is identical to PowerPC.

Differential Revision: https://reviews.llvm.org/D122676