This PR replaces our use of `__dso_handle` and (indirectly) `dladdr()`
when figuring out the base address of loaded Swift images on ELF-based
platforms. Instead, we use `__ehdr_start` which refers to the start of
the image's ELF header (i.e. the start of the file) and is provided by
the compiler/linker for this purpose.
This pointer is consumed by `swift_addNewDSOImage()` and, later, by
Swift Testing when running tests, but is otherwise unused, so the less
work we do on it at runtime, the better.
A fallback path is present that, for images that do not contain
`__ehdr_start`, derives the address by calling `dladdr()` on the section
structure's address.
Resolves#84997.
We'd still like to try to be forwardly compatible with future runtimes
that do properly handle noncopyable types, so emit them in a separate section from
copyable type records for now. This should prevent `_typeByName` from letting
someone get a hold of a noncopyable type's metatype as a (copyable) `Any.Type` and
then trying to use it to copy uncopyable values.
This replaces a number of `#include`-s like this:
```
#include "../../../stdlib/public/SwiftShims/Visibility.h"
```
with this:
```
#include "swift/shims/Visibility.h"
```
This is needed to allow SwiftCompilerSources to use C++ headers which include SwiftShims headers. Currently trying to do that results in errors:
```
swift/swift/include/swift/Demangling/../../../stdlib/public/SwiftShims/module.modulemap:1:8: error: redefinition of module 'SwiftShims'
module SwiftShims {
^
Builds.noindex/swift/swift/bootstrapping0/lib/swift/shims/module.modulemap:1:8: note: previously defined here
module SwiftShims {
^
```
This happens because the headers in both the source dir and the build dir refer to SwiftShims headers by relative path, and both the source root and the build root contain SwiftShims headers (which are equivalent, but since they are located in different dirs, Clang treats them as different modules).
