clang-cl: Invent a /winsysroot concept
On non-Windows platforms, --sysroot can be used to make the compiler use
a single, hermetic directory for all header and library files.
This is useful, but difficult to do on Windows. After D95472 it's
possible to achieve this with two flags:
out/gn/bin/clang-cl win.c -fuse-ld=lld \ /vctoolsdir path/to/VC/Tools/MSVC/14.26.28801 \ /winsdkdir path/to/win_sdk
But that's still cumbersome: It requires two flags instead of one, and
it requires writing down the (changing) VC/Tools/MSVC version.
This adds a new /winsysroot <dir> flag that's effectively an alias to
these two flags. With this, building against a hermetic Windows
toolchain only needs:
out/gn/bin/clang-cl win.c -fuse-ld=lld /winsysroot path
/winsysroot <dir> is the same as adding
/vctoolsdir <dir>/VC/Tools/MSVC/<vctoolsver> /winsdkdir <dir>/Windows Kits/<winsdkmajorversion>
<vctoolsver> is taken from /vctoolsversion if passed, or else it's
the name of the directory in <dir>/VC/Tools/MSVC that's the highest
<winsdkmajorversion> is the major version in /winsdkversion if passed,
else it's the name of the directory in <dir>/Windows Kits that's the
So /winsysroot <path> requires this subfolder structure:
path/ VC/ Tools/ MSVC/ 14.26.28801 (or another number) include/ ... Windows Kits/ 10/ Include/ 10.0.19041.0/ (or another number) um/ ... Lib/ 10.0.19041.0/ (or another number) um/ x64/ ... ...
Differential Revision: https://reviews.llvm.org/D95534