[clang] [Driver] Add support for -export-dynamic which can match GCC behavior. (PR #72781)

[Fangrui Song via cfe-commits]

MaskRay wrote:

GCC compatibility certainly matters a lot, but I feel that some of my previous points are ignored. My previous replies asked us to focus on other respects (a) whether the behavior makes sense or makes things more error-prone (b) whether not supporting it causes us trouble (c) whether the option has an alternative (d) ...

The facts that `-exxx`/`-e xxx` has been broken for so long up until I fixed it in 2020 and `-Wl,--export-dynamic`/`-rdynamic` are almost exclusively used mean a lot. The GCC PR says that (a) `-export-dynamic` was not supported in GCC (b) it worked was more of an accident (c) adding `-export-dynamic` was useful around 2011 when they needed to work with the problematic gawk use. If you have private software that uses `-export-dynamic`, can you fix it instead?

https://github.com/llvm/llvm-project/pull/72781