complibs/ppl: fix build when local system has libgmp already installed

Basically, the ppl configure script wasn't properly setting
CFLAGS/CXXFLAGS/LDFLAGS to point at the ctng-built gmp, so ppl tried to
use the system gmp headers instead.

This patch fixes that for all PPL versions supported by crosstools-ng.

Signed-off-by: Solomon Peachy <pizza@shaftnet.org>
[yann.morin.1998@free.fr: slightly touch the commit log]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Message-Id: <20130715230656.GB23382@shaftnet.org>
Patchwork-Id: 259300

 # Compute Blackfin-specific values

 CT_DoArchTupleValues() {

     # The architecture part of the tuple:

     CT_TARGET_ARCH="bfin${CT_ARCH_SUFFIX}"

     # gcc ./configure flags

     CT_ARCH_WITH_ARCH=

     CT_ARCH_WITH_ABI=

     CT_ARCH_WITH_CPU=

     CT_ARCH_WITH_TUNE=

     CT_ARCH_WITH_FPU=

     CT_ARCH_WITH_FLOAT=

 }