Cannot build WASM target on freebsd: 'errno.h' file not found

Summary

This broke somewhere after 2026-08-20 and 2026-08-30. Unfortunately, I cannot pinpoint exact broken version as versions right after that suffer from unrelated breakages.

Command used

After upding FreeBSD port lang/rust-nightly to the latest version (2026-08-20 with bootstraps 2026-08-28) , make -C /usr/ports/lang/rust-nigthly install

Expected behaviour

Successful build.

Actual behaviour

profiler_builtins fail to build for wasm target:

   Compiling profiler_builtins v0.0.0 (/work/usr/ports/lang/rust-nightly/work/rustc-nightly-src/library/profiler_builtins)
     Running `/work/usr/ports/lang/rust-nightly/work/_build/x86_64-unknown-freebsd/stage1-std/dist/build/profiler_builtins/72636cab5acea68e/out/build_script_build`
warning: profiler_builtins@0.0.0: /work/usr/ports/lang/rust-nightly/work/rustc-nightly-src/src/llvm-project/compiler-rt/lib/profile/GCDAProfiling.c:29:10: fatal error: 'errno.h' file not found
warning: profiler_builtins@0.0.0:    29 | #include <errno.h>
warning: profiler_builtins@0.0.0:       |          ^~~~~~~~~
warning: profiler_builtins@0.0.0: 1 error generated.
error: failed to run custom build command for `profiler_builtins v0.0.0 (/work/usr/ports/lang/rust-nightly/work/rustc-nightly-src/library/profiler_builtins)`

Notably, WASM target can be disabled in FreeBSD port, and rust builds fine if it is.

Bootstrap configuration (bootstrap.toml)

[build]
build-dir="/usr/ports/lang/rust-nightly/work/_build"
build-stage=2
doc-stage=2
test-stage=2
vendor=true
extended=true
python="/usr/local/bin/python3.12"
docs=false
verbose=2
profiler=true
target=["x86_64-unknown-freebsd","wasm32-unknown-unknown"]
cargo="/usr/ports/lang/rust-nightly/work/bootstrap/bin/cargo"
rustc="/usr/ports/lang/rust-nightly/work/bootstrap/bin/rustc"
tools=["analysis","cargo","clippy","rust-analyzer","rustdoc","rustfmt","src","miri","cargo-miri"]
ccache=false
[install]
prefix="/usr/ports/lang/rust-nightly/prefix"
sysconfdir="/usr/ports/lang/rust-nightly/prefix/etc"
[rust]
channel="nightly"
default-linker="cc"
deny-warnings=false
verbose-tests=true
download-rustc=false
lld=true
lto="thin"
remap-debuginfo=true
[llvm]
download-ci-llvm=false
clang=true
thin-lto=true
ninja=true
[target.x86_64-unknown-freebsd]
ar="ar"
cc="cc"
cxx="c++"
linker="cc"
[target.wasm32-unknown-unknown]
ar="ar"
cc="/usr/ports/lang/rust-nightly/work/_build/x86_64-unknown-freebsd/llvm/bin/clang"
cxx="/usr/ports/lang/rust-nightly/work/_build/x86_64-unknown-freebsd/llvm/bin/clang++"
linker="/usr/ports/lang/rust-nightly/work/_build/x86_64-unknown-freebsd/llvm/bin/clang"
[dist]
compression-formats=["xz"]
src-tarball=false

Operating system

FreeBSD 15.1

HEAD

cea272fa356e94bd2ee2cadf376630aa0683867a

Additional context

Full build log: https://people.freebsd.org/~amdmi3/rust.log
For reference, successful log for older version, 2026-08-20: https://people.freebsd.org/~amdmi3/rust20.log

Start with the failing profiler_builtins build and the compiler-rt file library/profiler_builtins invokes, src/llvm-project/compiler-rt/lib/profile/GCDAProfiling.c. Compare the wasm32-unknown-unknown compiler and linker settings in bootstrap.toml with the successful older build log and the failing log. Done means the FreeBSD port builds successfully with the WASM target enabled.