[Transform] fix legalization on absi (#310)

fix legalization on absi

Author: Ivy Zhang

lib/gc/Transforms/Pipeline.cpp

@@ -153,7 +153,7 @@ void populateLoweringToLLVMPasses(mlir::OpPassManager &pm) {
   pm.addPass(createConvertSCFToCFPass());
   pm.addPass(cpuruntime::createCPURuntimeToLLVM());
   pm.addPass(createConvertOpenMPToLLVMPass());
-  pm.addNestedPass<func::FuncOp>(createConvertMathToLLVMPass());
+  pm.addPass(createConvertMathToLLVMPass());
   pm.addPass(createConvertMathToLibmPass());
   pm.addNestedPass<func::FuncOp>(createArithToLLVMConversionPass());
   pm.addPass(createConvertVectorToLLVMPass());