[clang] [libc] [Clang] Fix cross-lane scan when given divergent lanes (PR #127703)

[Shilei Tian via cfe-commits]

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@@ -188,6 +186,32 @@ __DO_LANE_SCAN(float, uint32_t, f32);    // float __gpu_lane_scan_f32(m, x)
 __DO_LANE_SCAN(double, uint64_t, f64);   // double __gpu_lane_scan_f64(m, x)
 #undef __DO_LANE_SCAN
 
+// Gets the sum of all lanes inside the warp or wavefront.
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shiltian wrote:

nit: why do you need to sink this macro?

https://github.com/llvm/llvm-project/pull/127703