[LTO][clang] Using Single Dash Consistently when Passing LTO Options

The following three static functions in `clang/lib/Driver/ToolChains/CommonArgs.cpp`

```
static void renderRpassOptions(...)
static void renderRemarksOptions(...)
static void renderRemarksHotnessOptions(...)
```

use `--plugin-opt` for the plugin option prefix, while the function `tools::addLTOOptions`  uses `-plugin-opt`. This patch makes sure that we only use `-plugin-opt` (single dash) everywhere. It is not clear to me that why we decided to use `--plugin-opt` in https://reviews.llvm.org/D85810. If using `--plugin-opt` is intended, I'd love to hear the reason and I will close this patch.

We intend to followup this patch with a few other patches that teach `clang` to pass plugin options to the AIX linker, which uses a different prefix (`-bplugin_opt:`).

Reviewed By: w2yehia

Differential Revision: https://reviews.llvm.org/D134668