[clang] Implement -falign-loops=N (N is a power of 2) for non-LTO

GCC supports multiple forms of -falign-loops=.
-falign-loops= is currently ignored in Clang.

This patch implements the simplest but the most useful form where N is a
power of 2.

The underlying implementation uses a `llvm::TargetOptions` option for now.
Bitcode generation ignores this option.

Differential Revision: https://reviews.llvm.org/D106701