Add option to force filetype=asm for testing

tests_lit/llvm2ice_tests/strength-reduce.ll

Index: tests_lit/llvm2ice_tests/strength-reduce.ll
diff --git a/tests_lit/llvm2ice_tests/strength-reduce.ll b/tests_lit/llvm2ice_tests/strength-reduce.ll
index 50ca6e8ad63a87c5676a7d5dc362df2ab3261b97..c7ccb4fc3e419dc17fbc9bf80dc53752d088e04b 100644
--- a/tests_lit/llvm2ice_tests/strength-reduce.ll
+++ b/tests_lit/llvm2ice_tests/strength-reduce.ll
@@ -47,10 +47,8 @@ define internal i16 @mul_i16_arg_18(i16 %arg) {
   %result = mul i16 %arg, 18
   ret i16 %result
 }
-; Disassembly will look like "lea ax,[eax+eax*8]".
 ; CHECK-LABEL: mul_i16_arg_18
-; CHECK-DAG: lea [[REG:..]],{{\[}}e[[REG]]+e[[REG]]*8]
-; CHECK-DAG: shl [[REG]],1
+; CHECK: imul
 
 define internal i8 @mul_i8_arg_16(i8 %arg) {
   %result = mul i8 %arg, 16