pkg/59435: lang/rust fails to build on NetBSD 9.x (e.g., 9.4_STABLE) after the llvm 19 update

[david%gutteridge.ca@localhost]

>Number:         59435
>Category:       pkg
>Synopsis:       lang/rust fails to build on NetBSD 9.x (e.g., 9.4_STABLE) after the llvm 19 update
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    pkg-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue May 20 20:40:00 +0000 2025
>Originator:     David H. Gutteridge
>Release:        pkgsrc -current
>Organization:
TNF
>Environment:
>Description:
lang/rust fails to build on NetBSD 9.x (e.g., 9.4_STABLE) after the llvm 19 update.

This can be seen in bulk build reports, e.g.,
http://www.ki.nu/pkgsrc/reports/current/NetBSD-9.0/20250517.1036/rust-1.85.1nb3/build.log

   Compiling compiler_builtins v0.1.140
   Compiling rustc-std-workspace-core v1.99.0 (/tmp/lang/rust/work/rustc-1.85.1-src/library/rustc-std-workspace-core)
error: failed to prepare thin LTO module: Invalid alignment value (Producer: 'LLVM19.1.7' Reader: 'LLVM 19.1.7')

   Compiling alloc v0.0.0 (/tmp/lang/rust/work/rustc-1.85.1-src/library/alloc)
   Compiling cfg-if v1.0.0
   Compiling unwind v0.0.0 (/tmp/lang/rust/work/rustc-1.85.1-src/library/unwind)
error: could not compile `core` (lib) due to 1 previous error
warning: build failed, waiting for other jobs to finish...
error: failed to parse bitcode for LTO module: Invalid alignment value (Producer: 'LLVM19.1.7' Reader: 'LLVM 19.1.7')

error: could not compile `compiler_builtins` (lib) due to 1 previous error
error: could not compile `alloc` (lib) due to 1 previous error
Build completed unsuccessfully in 1:06:02

I can reproduce this in my 9.4_STABLE pbulk build environment.
>How-To-Repeat:
Try to build lang/rust.
>Fix:
I'm testing rebuilding using the (non-default) rust-internal-llvm option.