Fix zero-sized BTreeMap gdb pretty-printer

[artemmukhin]

gdb.parse_and_eval("()") is needed because GDB treats "()" as a Rust array of two characters, not as a unit

Based on intellij-rust/intellij-rust#6356

[rust-highfive]

r? @Mark-Simulacrum

(rust_highfive has picked a reviewer for you, use r? to override)

[Mark-Simulacrum]

@bors r+

[bors]

📌 Commit 4cf9369921407295bfb99a1c0e03737108f27ea5 has been approved by Mark-Simulacrum

[bors]

☔ The latest upstream changes (presumably #78104) made this pull request unmergeable. Please resolve the merge conflicts.

Note that reviewers usually do not review pull requests until merge conflicts are resolved! Once you resolve the conflicts, you should change the labels applied by bors to indicate that your PR is ready for review. Post this as a comment to change the labels:

@rustbot modify labels: +S-waiting-on-review -S-waiting-on-author

[Mark-Simulacrum]

tidy error: /checkout/src/etc/gdb_providers.py:232: line longer than 100 chars
tidy error: /checkout/src/etc/gdb_providers.py:233: line longer than 100 chars

CI seems to be failing here.

[artemmukhin]

@bors r=Mark-Simulacrum

[bors]

@ortem: 🔑 Insufficient privileges: Not in reviewers

[artemmukhin]

@Mark-Simulacrum r?

[Mark-Simulacrum]

@bors r+

[bors]

📌 Commit 685e1f3 has been approved by Mark-Simulacrum

[Mark-Simulacrum]

(For the future, if you want my attention on a PR, @rustbot modify labels: +S-waiting-on-review -S-waiting-on-author or similar (depending on current label) is the best way to get things back in my queue).

[bors]

⌛ Testing commit 685e1f3 with merge 92e4fb0...

[bors]

☀️ Test successful - checks-actions
Approved by: Mark-Simulacrum
Pushing 92e4fb0 to master...