Remove support for PowerPC SPE extension (powerpc*-*-*gnuspe*).

Remove support for PowerPC SPE extension (powerpc*-*-*gnuspe*).

GCC 9 dropped support for the SPE extensions to PowerPC, which means
powerpc*-*-*gnuspe* configurations are no longer buildable with that
compiler.  This ISA extension was peculiar to the “e500” line of
embedded PowerPC chips, which, as far as I can tell, are no longer
being manufactured, so I think we should follow suit.

This patch was developed by grepping for “e500”, “__SPE__”, and
“__NO_FPRS__”, and may not eliminate every vestige of SPE support.
Most uses of __NO_FPRS__ are left alone, as they are relevant to
normal embedded PowerPC with soft-float.

        * sysdeps/powerpc/preconfigure: Error out on powerpc-*-*gnuspe*
        host type.
        * scripts/build-many-glibcs.py: Remove powerpc-*-linux-gnuspe
        and powerpc-*-linux-gnuspe-e500v1 from list of build configurations.

        * sysdeps/powerpc/powerpc32/e500: Recursively delete.
        * sysdeps/unix/sysv/linux/powerpc/powerpc32/e500: Recursively delete.
        * sysdeps/unix/sysv/linux/powerpc/powerpc32/nofpu/context-e500.h:
        Delete.

        * sysdeps/powerpc/fpu_control.h: Remove SPE variant.
        Issue an #error if used with a compiler in SPE-float mode.
        * sysdeps/powerpc/powerpc32/__longjmp_common.S
        * sysdeps/powerpc/powerpc32/setjmp_common.S
        * sysdeps/unix/sysv/linux/powerpc/powerpc32/getcontext-common.S
        * sysdeps/unix/sysv/linux/powerpc/powerpc32/nofpu/getcontext.S
        * sysdeps/unix/sysv/linux/powerpc/powerpc32/nofpu/setcontext.S
        * sysdeps/unix/sysv/linux/powerpc/powerpc32/nofpu/swapcontext.S
        * sysdeps/unix/sysv/linux/powerpc/powerpc32/setcontext-common.S
        * sysdeps/unix/sysv/linux/powerpc/powerpc32/swapcontext-common.S:
        Remove code to preserve SPE register state.

        * sysdeps/unix/sysv/linux/powerpc/elision-lock.c
        * sysdeps/unix/sysv/linux/powerpc/elision-trylock.c
        * sysdeps/unix/sysv/linux/powerpc/elision-unlock.c
        Remove __SPE__ ifndefs.