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)

 This is a somewhat ordered TODO list:

 Recuring tasks:

 - update versions for every tools...

 - update and/or upgrade all samples

 Non-recurring tasks:

 - update newlib (for enhanced bare metal)

   - confirm existing implementation on targets other than AVR32

   - try to make it generic, will help for uClibc++

 - multilib

 - Cygwin target (needs newlib)

   - so we can build toolchains that generate code for Windows/Cygwin

 - Cygwin host

   - so we can build toolchains that run natively under Windows/Cygwin

 - mingw32 target

   - so we can build toolchains that generate code for Windows/Win32

 - mingw32 host

   - so we can build toolchains that run natively under Windows/Win32

     (without requiring Cygwin)

 - uClibc++

   - see newlib, above

 - uClinux

   - check whether we can use newlib under uClinux (?)