Make clang's --sysroot argument equivalent to clang-cl's /winsysroot argument on Windows targets

[godvino]

Right now clang's --sysroot argument doesnt do anything on Windows targets. I am cross compiling Windows applications from Linux (using Windows headers and libraries downloaded using xwin) and having to use a bunch of -I and -L flags isn't ideal. clang-cl's /winsysroot argument helps to reduce the number of arguments that should be passed while cross compiling but using clang-cl isn't ideal on non Windows systems partly because of its Windows-style arguments. It would be nice if clang's --sysroot argument became equivalent to the /winsysroot argument of clang-cl when target is set to Windows.

[llvmbot]

@llvm/issue-subscribers-clang-driver

[Qyriad]

Similarly it'd be excellent if clang supported equivalents to clang-cl's /winsdkdir and /vctoolsdir, though these probably couldn't be smooshed into existing options like /winsysroot can with --sysroot.

[trcrsired]

no. remove winsysroot

[Andarwinux]

just use -Xmicrosoft-windows-sys-root

[trcrsired]

Similarly it'd be excellent if clang supported equivalents to clang-cl's /winsdkdir and /vctoolsdir, though these probably couldn't be smooshed into existing options like /winsysroot can with --sysroot.

These setups are overly complex and lack support for libc++, making them practically useless. A GNU-style sysroot would solve everything, but Rust enthusiasts have complicated things by bringing in Cargo and micro-dependencies like xwin. I doubt xwin works well, especially since Microsoft's headers need fixes for case-sensitive filesystems—something that requires effort Microsoft isn't directly providing.

The last time I checked, even the Windows SDK has C headers mixed with standard C++ headers, and Microsoft's intrinsic headers don't work with Clang. Clang provides its own headers, like intrin.h, which aren't compatible with Microsoft's implementation.

I guess xwin is maintained by rust people who have very little knowledge on how things really work for C and C++, so you end up with even larger mess.

https://github.com/trcrsired/windows-msvc-sysroot