[llvm] [BasicBlockUtils] Remove redundant llvm.dbg instructions after blocks to reduce compile time (PR #89069)

[via llvm-commits]

coderchenlin wrote:

@fhahn, could you help me check this newly added case?
I reduced the IR generated by the https://github.com/llvm/llvm-project/issues/89073 and made some changes to make it clearer.

the loop body unrolls 5 times (full unroll) and generates the same 5 llvm.dbg instructions, with this change, there only has 1 llvm.dbg


https://github.com/llvm/llvm-project/pull/89069