Add in memory object files support to CompiledModule and ArchiveBuilder

[bjorn3]

https://doc.rust-lang.org/nightly/nightly-rustc/rustc_codegen_ssa/struct.CompiledModule.html

https://doc.rust-lang.org/nightly/nightly-rustc/rustc_codegen_ssa/back/archive/trait.ArchiveBuilder.html

rustc_codegen_cranelift can emit object files to memory without writing them to the disk. With the current setup they need to be written to the disk before an rlib can be created. This doubles the amount of data written to the disk compared to emitting the object files to memory and then creating an rlib file from that. Linking a dylib or executable will still need to write the object files to the disk, but at least rlibs don't have to anymore.

[hanna-kruppe]

Aside: LLVM also supports emitting object files into memory (just pass a raw_string_ostream instead of a raw_fd_ostream), so if this feature gets implemented for cranelift codegen and helps there, it might help LLVM codegen too.

[bjorn3]

We may want to only do this when the total size of all codegen units is below a certain threshold to reduce max-rss for big crates like script and rustc. (Assuming that LLVM performs the archive building in a streaming way like cg_clif.)

[bjorn3]

cc #104191 for the archive builder part