[llvm] [X86] Use an FP-based expansion for v4i32 ctlz on SSE2-only targets (PR #167034)

[Simon Pilgrim via llvm-commits]

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+; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu -mattr=+sse2,-ssse3 -o - | FileCheck %s
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RKSimon wrote:

all 3 of these new test files can be dropped - just regenerate the vector-lzcnt-128.ll checks with the update script

https://github.com/llvm/llvm-project/pull/167034