[gn build] Port 645e0dc

Author: llvmgnsyncbot

llvm/utils/gn/secondary/llvm/lib/Target/RISCV/BUILD.gn

@@ -165,6 +165,7 @@ static_library("LLVMRISCVCodeGen") {
     "RISCVVectorMaskDAGMutation.cpp",
     "RISCVVectorPeephole.cpp",
     "RISCVZacasABIFix.cpp",
+    "RISCVZilsdOptimizer.cpp",
   ]
 }