Sysroot compatibility?

I am attempting to build nginx with rules_foreign_cc 0.15.0. I have configured Bazel to use a hermetic C++ toolchain: toolchains_llvm 1.5.0, LLVM 20.1.0 and debian_bullseye_amd64_sysroot.tar.xz. When I attempt to build nginx with configure_make all programs produced by ./configure fail to link with the following error:

/usr/bin/ld: (.text+0x19): undefined reference to `__libc_csu_init'

When I remove the sysroot from C++ toolchain configuration, ./configure works as expected.

What could be the reason of that behaviour? Are rules_foreign_cc hermetic? The libc version in my sysroot is libc-2.31.so.

Start with the configure_make rule and the hermetic toolchain configuration described in the issue, using toolchains_llvm, LLVM 20.1.0, and debian_bullseye_amd64_sysroot.tar.xz. Reproduce the nginx configure failure with and without the sysroot and inspect the linker output around __libc_csu_init. Done means identifying the compatibility boundary and documenting a verified resolution or limitation.

Written by the indexing model from the issue text.