vm windows builds are broken

[aam]

Example of the failure https://logs.chromium.org/logs/dart/buildbucket/cr-buildbucket/8727606552166086897/+/u/build_dart/stdout

[2722/2746] CXX obj/samples/embedder/run_kernel.run_kernel.obj
FAILED: obj/samples/embedder/run_kernel.run_kernel.obj 
C:/opt/s/w/ir/cache/builder/sdk/buildtools/ninja/ninja -t msvc -e environment.arm64 -- "C:\opt\s\w\ir\cache\builder\sdk\win_toolchain\vs_files\27370823e7\VC\Tools\MSVC\14.34.31933\bin\Hostx64\arm64/cl.exe"  /nologo /showIncludes /FC -D__STD_C -D_CRT_RAND_S -D_CRT_SECURE_NO_DEPRECATE -D_HAS_EXCEPTIONS=0 -D_SCL_SECURE_NO_DEPRECATE -DWIN32_LEAN_AND_MEAN -DNOMINMAX -D_ATL_NO_OPENGL -D_WINDOWS -DCERT_CHAIN_PARA_HAS_EXTRA_FIELDS -DNTDDI_VERSION=0x0A000006 -DPSAPI_VERSION=1 -DWIN32 -D_SECURE_ATL -D_USING_V110_SDK71_ -D_UNICODE -DUNICODE -D_WIN32_WINNT=0x0603 -DWINVER=0x0603 -DDEBUG -I../../runtime -I../.. -Igen /Gy /GS /FS /WX /wd4091 /wd4722 /wd4312 /wd4838 /wd4172 /wd4005 /wd4311 /wd4477 /MTd /O2 /Oy- /Zi /Zc:__cplusplus /std:c++20 /std:c++20 /GR- /c ../../samples/embedder/run_kernel.cc /Foobj/samples/embedder/run_kernel.run_kernel.obj /Fdobj/samples/embedder/run_kernel_cc.pdb
c:\opt\s\w\ir\cache\builder\sdk\samples\embedder\run_kernel.cc(107) : error C2220: the following warning is treated as an error
c:\opt\s\w\ir\cache\builder\sdk\samples\embedder\run_kernel.cc(107) : warning C4700: uninitialized local variable 'error' used
[2723/2746] CXX arm64_shared/obj/runtime/bin/ffi_test/ffi_test_functions.ffi_test_functions.obj
[2724/2746] CXX obj/runtime/bin/dart_embedder_runtime_jit_set.dart_embedder_api_impl.obj
[2725/2746] CXX arm64_shared/obj/runtime/bin/ffi_test/ffi_test_functions.ffi_test_fu

seemingly starting with https://dart.googlesource.com/sdk/+/a7fe1e6f55cf910871e65640a49fa1bd9af065e3

cc @iinozemtsev

[aam]

https://dart-review.googlesource.com/c/sdk/+/402420 with proposed fix