completely eliminate dependency on LLD

[andrewrk]

In celebration of @kubkon's recent accomplishments of improving the self-hosted linker on Mach-O enough to be able to link LLVM, Clang, LLD, and Zig, this issue is to completely rely on our own linker implementation for all targets, and entirely stop linking against LLD. This issue is the spiritual successor to #1535.

• eliminate dependency on LLD for Mach-O #8727
• eliminate dependency on LLD for ELF #17749
• eliminate dependency on LLD for WebAssembly #17750
• eliminate dependency on LLD for COFF/PE #17751

Other Considerations

• miscellaneous features such as linker scripts (related: Linker scripts must die #3206)
• LTO. For our purposes, this would look like suporting LLVM IR bitcode files and using LLVM APIs to turn them into object(s) before completing the linking process.

[matthewp]

Does fixing #7133 need to wait on this? Will this issue fix that one?