Remove __signbit* from localplt.data as they are no longer called from within GLIBC.

	* sysdeps/unix/sysv/linux/aarch64/localplt.data: Remove __signbit*.
	* sysdeps/unix/sysv/linux/arm/localplt.data: Likewise.
	* sysdeps/unix/sysv/linux/microblaze/localplt.data: Likewise.
	* sysdeps/unix/sysv/linux/nios2/localplt.data: Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc32/nofpu/localplt.data: Likewise.