[MemCpyOpt] Remove libcall availability checks for memory intrinsics (#198558)
Fixes #197683
- Delete the enable-memcpyopt-without-libcalls flag from MemCpyOptimizer
- Remove libcall availability checks in processStoreOfLoad() and
processStore()
- Remove the flag from CUDA/OpenMP toolchain in Clang
- Update no-libcalls.ll test to expect optimizations on all targets
cc @arsenm
Signed-off-by: addmisol <addmisol9@gmail.com>