cxxmodules: Support `import std` for msvc-wine
https://github.com/mstorsjo/msvc-wine/pull/126 proposes below msvc-wine installation layout for modules:
${root}/bin/x64/cl.exe
${root}/modules/modules.json
which is different from the original VCToolsInstallDir layout:
${VCToolsInstallDir}/bin/Hostx64/x64/cl.exe
${VCToolsInstallDir}/modules/modules.json
This MR make it able to find modules.json
in msvc-wine toolchain without any environment variables presets.