Fix multiton issue

I385a05a3ca01258e44fe3b37ef77e4aaff547b26 broke Singleton in the
same way that 544e3e36 had already
fixed once.  Fix it again, the next CL will add tests.

This affected cases where two libraries referenced the same singleton,
the one that was supposed to define the singleton was already loaded,
and then the second library was dlopen'd.

Bug: 35674422
Test: out/host/linux-x86/nativetest64/libutils_tests/libutils_tests
      from later CL
Change-Id: I87c64f95ed294a887e67a6c11be3072299789f01