[llvm] Fix merging of debug_str_offsets with multiple contributions (PR #90461)

[Morten larsen via llvm-commits]

molar wrote:

> Thanks!
> 
> Generally I think we're moving away from checked in binary object files - could you make the test from checked in assembly instead (perhaps using @MaskRay's new https://llvm.org/docs/TestingGuide.html#elaborated-tests perhaps)
> 
> So if I'm understanding correctly - you're saying llvm-dwp did not work when an input was a DWP and was DWARFv5? huh, surprising oversight... oh, I guess not that many people use dwp files as input to dwp actions, so I can see how some people would've been working along fine with this state of affairs.

Thank you for looking at this PR. 

We encounter this bug when using bazel along with llvm-dwp tool to generate .dwp files for our top-level binaries. In bazel it will switch to a tree merging when the number of .dwo inputs is larger than 100. It does not use the `-e` flag together with the binary which does the correct thing.  

https://github.com/bazelbuild/bazel/blob/7048ef5eb5395679241f2321a8104b26ecee01c0/src/main/starlark/builtins_bzl/common/cc/cc_debug_helper.bzl#L129



https://github.com/llvm/llvm-project/pull/90461