[Bug 2120727] [NEW] "Multi-Arch: same" is required for core libllvm19 library

[Rob Savoury]

Public bug reported:

In the changelog for src:llvm-toolchain-19 version 1:19.1.7-5ubuntu1 is
this entry:

"Drop Multi-Arch: same from packages installing to non-multiarch paths.
(Closes: #1100981)"

While it is correct to do this for the Clang/LLVM packages that do
install arch dependent binaries to non-multiarch paths, for some reason
this change was also applied to the core libllvm19 library package. It
is not correct to remove "Multi-Arch: same" from that package (as no
arch specific binaries are installed to non-multiarch paths) and doing
so actually breaks the ability to co-install libllvm19:i386, which is a
required dependency for certain other software (ie. Steam app).

Restoring "Multi-Arch: same" to the libllvm19 package fixes the co-
installation issue, as is done with the attached patch file. It would be
good to fix this issue in src:llvm-toolchain-19 prior to the release of
Ubuntu 25.10 Questing Quokka.

** Affects: llvm-toolchain-19 (Ubuntu)
     Importance: Undecided
         Status: New

** Patch added: "libllvm19-multiarch-same.patch"
   https://bugs.launchpad.net/bugs/2120727/+attachment/5899387/+files/libllvm19-multiarch-same.patch

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https://bugs.launchpad.net/bugs/2120727

Title:
  "Multi-Arch: same" is required for core libllvm19 library

Status in llvm-toolchain-19 package in Ubuntu:
  New

Bug description:
  In the changelog for src:llvm-toolchain-19 version 1:19.1.7-5ubuntu1
  is this entry:

  "Drop Multi-Arch: same from packages installing to non-multiarch
  paths. (Closes: #1100981)"

  While it is correct to do this for the Clang/LLVM packages that do
  install arch dependent binaries to non-multiarch paths, for some
  reason this change was also applied to the core libllvm19 library
  package. It is not correct to remove "Multi-Arch: same" from that
  package (as no arch specific binaries are installed to non-multiarch
  paths) and doing so actually breaks the ability to co-install
  libllvm19:i386, which is a required dependency for certain other
  software (ie. Steam app).

  Restoring "Multi-Arch: same" to the libllvm19 package fixes the co-
  installation issue, as is done with the attached patch file. It would
  be good to fix this issue in src:llvm-toolchain-19 prior to the
  release of Ubuntu 25.10 Questing Quokka.

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