Allow _Qp_fgt in sparc64 localplt.data

A recent GCC change resulted in localplt test failures on sparc64
because of references to _Qp_fgt.  This is analogous to all the other
floating-point symbols allowed in localplt.data, so it seems
appropriate to allow this one as well.

Tested with build-many-glibcs.py for sparc64-linux-gnu (GCC mainline),
where it fixes the test failure.