try different stdc++ linker

lakefile.lean

@@ -17,9 +17,9 @@ target datetime.o pkg : FilePath := do
   let oFile := pkg.buildDir / "DateTime" / "c" / "datetime.o"
   let srcJob ← inputFile <| pkg.dir / "DateTime" / "c"  / "datetime.cpp"
   let weakArgs := #["-I", (← getLeanIncludeDir).toString]
-  buildO "datetime.cpp" oFile srcJob weakArgs #["-fPIC", "-lstdc++"] (compiler := "cc") getLeanTrace
+  buildO "datetime.cpp" oFile srcJob weakArgs #["-fPIC", "-lstdc++.so.6"] (compiler := "cc") getLeanTrace
 
-extern_lib lib_datetime pkg := do
+extern_lib libleandatetime pkg := do
   let name := nameToStaticLib "datetime"
   let datetimeO ← fetch <| pkg.target ``datetime.o
   buildStaticLib (pkg.nativeLibDir / name) #[datetimeO]