[LoongArch] Align stack objects passed to memory intrinsics (#101309)
Memcpy, and other memory intrinsics, typically try to use wider
load/store if the source and destination addresses are aligned. In
CodeGenPrepare, look for calls to memory intrinsics and, if the object
is on the stack, align it to 4-byte (32-bit) or 8-byte (64-bit)
boundaries if it is large enough that we expect memcpy to use wider
load/store instructions to copy it.
Fixes #101295