Replace use of mkstemps with mkstemp to accomodate glibc < 2.11

I don't like it, but right now, my stuff is the only thing in libMesh, that requires a glibc version >=2.11

I have replaced the ```mkstemps``` (temp file with extension) with ```mkstemp``` (no extension). I do have to do some file renaming now, to make sure that the compiler gets a file with a correct suffix.
```stdlib.h``` is included above anyways.