unknown codegen option: `-Zshare-generics`

[probablykasper]

Describe the bug

Just wanted to try fleet out, but getting an error even though I'm using nightly:

📝 Generated Fleet Config
🚀 Fleet is ready!
error: failed to run `rustc` to learn about target-specific information

Caused by:
  process didn't exit successfully: `rustc - --crate-name ___ --print=file-names -C -Zshare-generics=y -Csplit-debuginfo=unpacked -C -Zshare-generics=y -Csplit-debuginfo=unpacked --crate-type bin --crate-type rlib --crate-type dylib --crate-type cdylib --crate-type staticlib --crate-type proc-macro --print=sysroot --print=cfg` (exit status: 1)
  --- stderr
  error: unknown codegen option: `-Zshare-generics`

To Reproduce
fleet build

Info:

• OS: macOS 10.15
• rustc: rustc 1.64.0-nightly (4d6d601c8 2022-07-26)
• Fleet: 8dce51c