[llvm] [DebugInfo][DWARF] Set is_stmt on first non-line-0 instruction in BB (PR #105524)

[Stephen Tozer via llvm-commits]

SLTozer wrote:

Updated a couple more tests whose outputs have changed as of the latest functional change - all of these look "correct" to me, in that they're adding is_stmt to instructions at the start of a basic block, or in `empty-inline.mir`, adding a few new entries that prevent a line-0 instruction at the start of a basic block from having a non-0 fallthrough location, and adding a new is_stmt entry at the start of a block (similar to the case in the initial report).

https://github.com/llvm/llvm-project/pull/105524