Announced on https://lists.llvm.org/pipermail/llvm-dev/2020-May/141416.html
For many options, we have to support either one or two dash to be
compatible with GNU ld. For newer and lld specific options, we can enforce strict double dashes.
Affected options:
- --thinlto-*
- --lto-*
- --shuffle-sections=
This patch does not change -plugin-opt=* because clang driver passes
-plugin-opt=* and I don't intend to cause churn.
In 2000, GNU ld tried something similar
https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=e4897a3288f37d5f69e8acd256a6e83e607fe8d8