llvm-clang-win-x-{armv7l,aarch64}-release: migrate away from DEFAULT_SYSROOT #94284
Description
The CMake variable DEFAULT_SYSROOT provides a default --sysroot= for every clang --target=xxx.
Within the clang/test/Driver testsuite, there have been many changes tha adjust --sysroot= so that
these tests will pass on build bots that specify DEFAULT_SYSROOT.
Like the now-deprecated GCC_INSTALL_PREFIX, this places undue maintenance burden to keep clang/test/Driver tests pass for all supported bots.
Two changes should happen:
- There should be no expectation that all tests will pass.
DEFAULT_SYSROOTshould eventually be deprecated and then removed. (After we figure out a way to support relative paths https://reviews.llvm.org/D158218)
As alternatives, llvm-clang-win-x-{armv7l,aarch64}-release may switch a Clang configuration file.
- https://clang.llvm.org/docs/UsersManual.html#configuration-files
- https://blogs.gentoo.org/mgorny/2022/10/07/clang-in-gentoo-now-sets-default-runtimes-via-config-file
In short, place bin/$default_triple.cfg beside bin/clang.
clang/test/lit.cfg.py specifies config.environment["CLANG_NO_DEFAULT_CONFIG"] = "1", so the configuration files will not affect %clang behavior in driver tests.