Andrew Marshall 937266f668
use a libcxx abi namespace compatible with lldb (#180134)
LLDB's type formatters expect the libcxx ABI namespace to start with two
leading underscores.

See [LLDB Discourse
Thread](https://discourse.llvm.org/t/lldb-type-summaries-not-displayed-for-libcxx-types/88447)
and [LLDB
Sources](5099c07fa0/lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp (L761))

Fixes #180132

Note that this change requires a complete rebuild of the engine sources
- see related #180128

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] All existing and new tests are passing.
2026-01-05 21:31:10 +00:00
..
2025-09-30 00:57:09 +00:00
2025-07-23 16:56:43 +00:00