[clang] [clang] Fix --entry command line option (PR #69114)

[Fangrui Song via cfe-commits]

MaskRay wrote:

Since `--entry` is wrong, `--entry=` is unsupported, and nobody seems to use the driver option which only affects linking, we probably should just remove it. Users are expected to use `-Wl,-e,entry` or `-Wl,--entry=entry` anyway.

https://github.com/llvm/llvm-project/pull/69114