[clang][LTO] Remove the use of `--` for arange option

https://reviews.llvm.org/D134668 removed all `--` (double dashes) when using `plugin-opt` to pass linker options and replaced them with `-`. https://reviews.llvm.org/D133092 was committed later but introduced an instance of `--`. This patch replaces the `--` with `-`.

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D135400