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)

scripts/build/companion_libs/ppl.sh

@@ -41,6 +41,7 @@ do_ppl() {
         --prefix="${CT_COMPLIBS_DIR}"               \
         --with-libgmp-prefix="${CT_COMPLIBS_DIR}"   \
         --with-libgmpxx-prefix="${CT_COMPLIBS_DIR}" \
+        --with-gmp-prefix="${CT_COMPLIBS_DIR}"      \
         --enable-cxx                                \
         --enable-watchdog                           \
         --disable-debugging                         \