Update nios2, sparc32 localplt.data files for recent GCC change.

A recent GCC change to expand floating-point classification built-in
functions inline using integer rather than floating-point arithmetic
in some cases resulted in localplt test failures for nios2 and sparc32
<https://sourceware.org/ml/libc-testresults/2017-q2/msg00320.html>.
This patch updates the localplt.data files in question to mark the
relevant symbols as optional / add a new optional symbol.  (The GCC
patch has been reverted because of other problems it caused, but one
can assume it will be applied again, without changes that would affect
the PLT entries generated, once those issues have been resolved.)

Tested with build-many-glibcs.py.

	* sysdeps/unix/sysv/linux/nios2/localplt.data (__gtdf2): Mark
	libc.so PLT entry optional.
	(__gtsf2): Likewise.
	(__unorddf2): Likewise.
	(__unordsf2): Likewise.
	* sysdeps/unix/sysv/linux/sparc/sparc32/localplt.data (_Q_fgt):
	New optional libc.so PLT entry.