fix lit file

Author: Shoreshen

llvm/test/lit.cfg.py

@@ -466,7 +466,7 @@ def have_cxx_shared_library():
         print("could not exec llvm-readobj")
         return False
 
-    readobj_out = readobj_cmd.stdout.read().decode("utf-8")
+    readobj_out = readobj_cmd.stdout.read().decode("ascii")
     readobj_cmd.wait()
 
     regex = re.compile(r"(libc\+\+|libstdc\+\+|msvcp).*\.(so|dylib|dll)")