Limit target endian to an enum instead of free string

[tesuji]

This is #77604 revived.

[petrochenkov]

If you're still not satisfied with that respond, I will remove them.

Yes, could you remove them.
Otherwise, LGTM.

[tesuji]

I removed the micro methods.
@rustbot label: -S-waiting-on-author +S-waiting-on-review

[petrochenkov]

Thanks!
@bors r+

[bors]

📌 Commit 8ee804d has been approved by petrochenkov

[bors]

⌛ Testing commit 8ee804d with merge 7e62e32b79236a0f7199354000afba0836e4deba...

[rust-log-analyzer]

The job mingw-check failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

Build completed successfully in 0:00:55
+ /scripts/validate-toolstate.sh
Cloning into 'rust-toolstate'...
<Nothing changed>
error: book maintainer @carols10cents is not assignable in the rust-lang/rust repo

  To be assignable, a person needs to be explicitly listed as a
  collaborator in the repository settings. The simple way to
  fix this is to ask someone with 'admin' privileges on the repo
  to add the person or whole team as a collaborator with 'read'
  privileges. Those privileges don't grant any extra permissions
  so it's safe to apply them.
The build will fail due to this.

[bors]

💔 Test failed - checks-actions

[petrochenkov]

error: book maintainer @carols10cents is not assignable in the rust-lang/rust repo

@bors retry

[bors]

⌛ Testing commit 8ee804d with merge e02b0f4...

[bors]

☀️ Test successful - checks-actions
Approved by: petrochenkov
Pushing e02b0f4 to master...