Fix creation of libperl519s.a on Win32 with MinGW

Fix creation of libperl519s.a on Win32 with MinGW

The "ar rc" command created an invalid static perl library by putting the
static extension libraries themselves into the library rather than putting
the objects from each static extension library into it as intended (like
the VC++ "link -lib" command does).

We now extract each static extension library's objects into a temporary
directory and put the objects from there into the static perl library.