Make MSVC STL data formatters for Windows

[llvmbot]

Bugzilla Link	24460
Version	unspecified
OS	Windows NT
Depends On	#24836
Blocks	#22140
Reporter	LLVM Bugzilla Contributor
CC	@amccarth-google

Extended Description

Currently LLDB only supports data formatters for libc++. Since libc++ isn't a thing on Windows, we need to add data formatters for MSVC's STL implementation under test/data-formatter/data-formatter-stl/msvc which test similar functionality to the ones for the other stl implementations.

[llvmbot]

mentioned in issue #24836

[Nerixyz]

#120310 had some thoughts about this topic, so I'll try to summarize.

Curently, the main issue is that libstdc++ and MSVC's STL use the same type names. Or rather: neither of them uses an inline namespace. This makes it hard to distinguish the two, as matching is done by the type name. A name like std::optional<T> would resolve in both STLs.
In the linked issue, this resulted in crashes when using MSVC's STL where LLDB tried to access members only present in libstdc++.

Some ideas on how to move forward:

In #120310 (comment), Michael137 mentions that STL vendors could include a symbol to distinguish the implementations.
One thing I observed is that executables on Windows that link with MSVC/VC libs usually have a symbol starting with __vcrt.
C++ PDBs specifically should include a typedef bool __vcrt_bool; which is included through <vcruntime.h> (included here). Even a simple program compiled with clang-cl -Xclang -debug-info-kind=limited includes that typedef in the PDB.

To my knowledge, this would require that a subset of formatters in the cplusplus category could be dynamically switchable.
Having separate categories for each standard library would've been great here. Maybe there could be some "supercategory" cplusplus that managed other categories (libc++, libstdc++ etc.)? This should be backwards compatible (i.e. doing type category disable cplusplus would still work). Only adding types to that category would break.
Even if the vcrt "hack" doesn't work, this could be nice where LLDB could check if the target is *-windows-msvc and use MSVC STL types but use libstdc++ types elsewhere (namely on *-windows-gnu).

For completeness, in VS' debugger/NatVis, types can be tied to a module and different formatters cascade if one fails (each one has to have a different priority in that case). This could be helpful if users debug applications that (through DLLs) link to both STLs. I'd expect this use-case to be really rare, though.

[DavidSpickett]

Related Discourse discussion - https://discourse.llvm.org/t/formatting-msvc-stl-types/86667

[DavidSpickett]

Since libc++ isn't a thing on Windows

To be clear, Windows is now supported, but this feature request is valid regardless. The majority of programs are probably using MSVC STL.