Make dependency_formats an FxIndexMap rather than a list of tuples

It is treated as a map already. This is using FxIndexMap rather than
UnordMap because the latter doesn't provide an api to pick a single
value iff all values are equal, which each_linked_rlib depends on.

Author: bjorn3

src/driver/jit.rs

@@ -287,12 +287,7 @@ fn dep_symbol_lookup_fn(
 
     let mut dylib_paths = Vec::new();
 
-    let data = &crate_info
-        .dependency_formats
-        .iter()
-        .find(|(crate_type, _data)| *crate_type == rustc_session::config::CrateType::Executable)
-        .unwrap()
-        .1;
+    let data = &crate_info.dependency_formats[&rustc_session::config::CrateType::Executable].1;
     // `used_crates` is in reverse postorder in terms of dependencies. Reverse the order here to
     // get a postorder which ensures that all dependencies of a dylib are loaded before the dylib
     // itself. This helps the dynamic linker to find dylibs not in the regular dynamic library