Error when Cross-Compiling from WSL Ubuntu to Win32 - c++

Question

I'm writing a lot of cross platform C++, and am trying to unify my build process between platforms (primarily targeting Windows and Mac at the moment, potentially mobile in the future.) In addition to our normal CI builds, we are built from source as part of an extremely large C++ project's build and consequently have quite a complex toolchain.
Right now, my code compiles cleanly on Windows using CMake to generate a Visual Studio project and then using clang-cl to compile. Similarly, we are using CMake to generate a ninja project and then clang to compile.
We are a Windows shop, and I would like to leverage WSL to set up cross compilation, which should allow us to use the same ninja project to target both supported platforms and modify in the future.
I am able to successfully compile a simple hello world exe program using clang from my wsl-hosted bash terminal. In order to do this, I had to provide a large amount of options to clang as well as move a significant amount of Win10 SDK libraries to my build environment for clang to build and link against.
Here are the two commands I run to successfully produce helloworld.exe:
Compiling:
clang -target i686-pc-win32 -fms-compatibility-version=19 -fms-extensions -fdelayed-template-parsing -fexceptions -mthread-model posix -fno-threadsafe-statics -Wno-msvc-not-found -DWIN32 -D_WIN32 -D_MT -D_DLL -Xclang -disable-llvm-verifier -Xclang '--dependent-lib=msvcrt' -Xclang '--dependent-lib=ucrt' -Xclang '--dependent-lib=oldnames' -Xclang '--dependent-lib=vcruntime' -D_CRT_SECURE_NO_WARNINGS -D_CRT_NONSTDC_NO_DEPRECATE -U__GNUC__ -U__gnu_linux__ -U__GNUC_MINOR__ -U__GNUC_PATCHLEVEL__ -U__GNUC_STDC_INLINE__ -I/mnt/d/source/windeps/LLVM/include -I/mnt/d/source/windeps/MSVC/14.22.27905/include -I/mnt/d/source/windeps/ucrt -I/mnt/d/source/windeps/shared -I/mnt/d/source/windeps/winrt -c hello.cc -o hello.o
Linking:
clang -fuse-ld=lld-link.exe -target i686-pc-win32 -Wl,-machine:x86 -fmsc-version=1923 -o hello.exe hello.o -L/mnt/d/source/windeps/MSVC/14.22.27905/lib/x86/msvcrt.lib -nostdlib -lmsvcrt -Wno-msvc-not-found
Naturally, I have attempted to express this first command via my CMake toolchain:
add_compile_options(
-W
-Wall
-std=c++17
-stdlib=libc++
-fcoroutines-ts
-fms-extensions
-fdelayed-template-parsing
-fexceptions
-fdeclspec
-mthread-model posix
-fno-threadsafe-statics
-Wno-msvc-not-found
-DWIN32
-D_WIN32
-D_MT
-D_DLL
-Xclang
-disable-llvm-verifier
# These are commented out currently, but I have linked them to the proper CMakeList
# -Xclang '--dependent-lib=msvcrt'
# -Xclang '--dependent-lib=ucrt'
# -Xclang '--dependent-lib=oldnames'
# -Xclang '--dependent-lib=vcruntime'
-D_CRT_SECURE_NO_WARNINGS
-D_CRT_NONSTDC_NO_DEPRECATE
-U__GNUC__
-U__gnu_linux__
-U__GNUC_MINOR__
-U__GNUC_PATCHLEVEL__
-U__GNUC_STDC_INLINE__
-I/mnt/d/source/windeps/LLVM/include
-I/mnt/d/source/windeps/MSVC/14.22.27905/include
-I/mnt/d/source/windeps/um
-I/mnt/d/source/windeps/ucrt
-I/mnt/d/source/windeps/shared
-I/mnt/d/source/windeps/winrt
)
This is throwing an error from within the ucrt library when one of our files (event_logger.cpp) does #include <array>.
In file included from src/client/services/src/event_logger.cpp:10:
In file included from /mnt/d/source/windeps/MSVC/14.22.27905/include/array:6:
In file included from /mnt/d/source/windeps/MSVC/14.22.27905/include/algorithm:6:
In file included from /mnt/d/source/windeps/MSVC/14.22.27905/include/xmemory:8:
In file included from /mnt/d/source/windeps/MSVC/14.22.27905/include/limits:8:
In file included from /mnt/d/source/windeps/MSVC/14.22.27905/include/cwchar:8:
In file included from /mnt/d/source/windeps/MSVC/14.22.27905/include/cstdio:8:
In file included from /mnt/d/source/windeps/ucrt/stdio.h:13:
/mnt/d/source/windeps/ucrt/corecrt_wstdio.h:581:9: error: use of undeclared identifier '__crt_va_end'
__crt_va_end(_ArgList);
^
/mnt/d/source/windeps/ucrt/corecrt_wstdio.h:597:9: error: use of undeclared identifier '__crt_va_start_a'
__crt_va_start(_ArgList, _Locale);
^
/mnt/d/source/windeps/MSVC/14.22.27905/include/vadefs.h:156:99: note: expanded from macro '__crt_va_start'
#define __crt_va_start(ap, x) ((void)(__vcrt_assert_va_start_is_not_reference<decltype(x)>(), __crt_va_start_a(ap, x)))
Because of this behavior, I'm suspicious that perhaps we're not using libc++ as indicated by the -stdlib flag. I'm also not sure how to correct this, as this seems to be kind of a newer process and there's not a ton of documentation in the wild yet. Any advice is appreciated.