without relying on spare bit information in the reflection metadata
(which was added in #40906). As a result, we can remove the
code from #40906.
This is the first step in such removal. It removes the RemoteMirror
code for looking up such metadata. It leaves behind:
* Sufficient stubs for LLDB to continue to build. Once LLDB is updated, these stubs can be removed as well.
* The compiler code to emit such metadata. This allows new binaries to still reflect MPEs on older runtimes. This will need to be kept for a transitional period.
This change enables the `--gc-sections` linker flag for WebAssembly
targets by default. This flag has been disabled because it did not
respect `llvm.used` and it caused stripping `swift5` metadata sections
even though they were used through encapsulation symbols (a.k.a `__start`/`__stop`).
The issue has been fixed in the LLVM side (ba3c1f9ce3)
by adding new segment flags to the WebAssembly object file format.
When we're statically linking the standard library, we need to force
the inclusion of the backtracing code in the runtime, otherwise we don't
get on-crash backtraces.
Also, add a test to make sure that this works.
rdar://115774613
