Change namespace llvm::swift to namespace llvm::binaryformat because of...

Change namespace llvm::swift to namespace llvm::binaryformat because of clashes with the apple/llvm-project repository

The namespace llvm::swift is causing errors to pop up in the apple/llvm-project build when cherry-picking 4ce1f3d4 into apple/llvm-project

Differential Review: https://reviews.llvm.org/D118716