This patch ensures we can find decls in submodules during expression
evaluation. Previously, submodules would have all their decls marked as
`Hidden`. When Clang asked LLDB for decls, it would see them in the
submodule but `clang::Sema` would reject them because they weren't
`Visible` (specifically, `getAcceptableDecl` would fail during
`CppNameLookup`). Here we just mark the submodule as visible to work
around this problem.
Or more precisely, when linking with link.exe, but Windows
is our closest proxy for that right now.
This test requires the DWARF info to work, on the Windows on Arm
buildbot it fails:
```
AssertionError: Ran command:
"expr func(1, 2)"
Got output:
error: <user expression 0>:1:1: use of undeclared identifier 'func'
1 | func(1, 2)
| ^~~~
Expecting start string: "error: <user expression 0>:1:1: 'func' has unknown return type" (was not found)
```
Inferred submodule declarations are emitted in DWARF as `DW_TAG_module`s
without `DW_AT_LLVM_include_path`s. Instead the parent DIE will have the
include path. This patch adds support for such setups. Without this, the
`ClangModulesDeclVendor` would fail to `AddModule` the submodules (i.e.,
compile and load the submodules). This would cause errors such as:
```
note: error: Header search couldn't locate module 'TopLevel'
```
The test added here also tests
https://github.com/llvm/llvm-project/pull/141220. Without that patch
we'd fail with:
```
note: error: No module map file in /Users/jonas/Git/llvm-worktrees/llvm-project/lldb/test/API/lang/cpp/decl-from-submodule
```
Unfortunately the embedded clang instance doesn't allow us to use the
decls we find in the modules. But we'll try to fix that in a separate
patch.
rdar://151022173
