complibs/ppl: update GMP location configuration argument for PPL v0.11 and later

'configure' for PPL 0.11 (and later) needs "--with-gmp-prefix" to
provide the location of the GMP toolkit; the previous switches were
"--with-libgmp-prefix" and "--with-libgmpxx-prefix".

The upstream log message is:

commit 08dfb6fea094f8c5a533575a3ea2095edce99a6d
Author: Roberto Bagnara <bagnara@cs.unipr.it>
Date: Sun Jul 12 21:39:46 2009 +0200

New configure option --with-gmp-prefix supersedes the (now removed)
options --with-libgmp-prefix and --with-libgmpxx-prefix.

Link: http://www.cs.unipr.it/git/gitweb.cgi?p=ppl/ppl.git;a=commit;h=08dfb6fea094f8c5a533575a3ea2095edce99a6d

Since PPL's 'configure' ignores unknown switches, we use all three so we
don't have to conditionalize the ppl.sh build script itself.

Signed-Off-By: Anthony Foiani <anthony.foiani@gmail.com>
(transplanted from 4f0c4fb572e2862c24b28e8d27ce7e9cb9adba65)

# Configuration file for sstrip tool facility

if OBSOLETE && ! BACKEND && ARCH_BINFMT_ELF

comment "sstrip"

config SSTRIP

    bool

    prompt "sstrip (OBSOLETE)"

    help

      The sstrip utility, to maximise the striping of ELF binaries

      (executables and libraries).

      Buildroot version, forked off the original from ELFkickers.

      This one is somewhat maintained by the buildroot guys.

      Supports big-endian systems.

      NOTE! Please read.

        sstrip is now deprecated in crosstool-NG, as it has a few

        shortcomings. For example: it breaks for PPC targets, it

        does not build on non-ELF hosts (eg. mingw32, MacOS-X...).

endif