attempting to build on NetBSD/amd64 9.99.81 causes boootstrap/debug/rustc to crash with a SIGSEGV

I've been attempting to build rust from a clone done today (HEAD is 3736b85779d1db4c215b910004d7efcd7aff8408) on NetBSD/amd64 9.99.81 and I'm seeing boootstrap/debug/rustc crash with a SIGSEGV while "Building stage1 library artifacts".

./configure --set install.prefix=/usr/local --set install.sysconfdir=/usr/local/etc

Then because I didn't want to build LLVM I added the following line to the [llvm] section of the generated ./config.toml:

download-ci-llvm = true

Running ./x.py build results in:

   Compiling llvm-bitcode-linker v0.0.1 (/work/woods/m-rust/src/tools/llvm-bitcode-linker)
    Finished `release` profile [optimized] target(s) in 26.06s
Building stage1 library artifacts (x86_64-unknown-netbsd)
error: failed to run `rustc` to learn about target-specific information

Caused by:
  process didn't exit successfully: `/work/woods/m-rust/build/bootstrap/debug/rustc /work/woods/m-rust/build/bootstrap/debug/rustc - --crate-name ___ --print=file-names -Csymbol-mangling-version=legacy '--check-cfg=cfg(feature,values(any()))' -Zunstable-options '--check-cfg=cfg(bootstrap)' -Zmacro-backtrace -Csplit-debuginfo=off -Cprefer-dynamic -Zinline-mir -Zinline-mir-preserve-debug -Zmir_strip_debuginfo=locals-in-tiny-functions -Clink-args=-Wl,-z,origin '-Clink-args=-Wl,-rpath,$ORIGIN/../lib' -Cembed-bitcode=yes -Cforce-frame-pointers=yes '-Zcrate-attr=doc(html_root_url="https://doc.rust-lang.org/nightly/")' --target x86_64-unknown-netbsd --crate-type bin --crate-type rlib --crate-type dylib --crate-type cdylib --crate-type staticlib --crate-type proc-macro --print=sysroot --print=split-debuginfo --print=crate-name --print=cfg` (exit status: 254)
  --- stderr
  rustc exited with signal: 11 (SIGSEGV) (core dumped)
Build completed unsuccessfully in 0:18:05

GDB 11.0 can't find any symbols to give a reasonable stack backtrace from the resulting core (despite file reporting that the binary is "not stripped").

Reproduce the failure from the reported Rust revision using the NetBSD/amd64 target, the generated config.toml with download-ci-llvm enabled, and ./x.py build. Start with build/bootstrap/debug/rustc and the failed target-information command, then use GDB on the core if possible. Done means rustc no longer exits with SIGSEGV while building stage1 library artifacts.