Make constant arrays that are passed to functions as const.

Make constant arrays that are passed to functions as const.

In theory this allows the compiler to skip materializing the array on
the stack. In practice clang often fails to do that, but that's a
different story. NFC.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@231571 91177308-0d34-0410-b5e6-96231b3b80d8