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

 CT_EXPERIMENTAL=y

 CT_LOCAL_TARBALLS_DIR="${HOME}/src"

 CT_SAVE_TARBALLS=y

 CT_LOG_EXTRA=y

 CT_ARCH_ARCH="i686"

 CT_ARCH_TUNE="i686"

 CT_ARCH_x86=y

 CT_TARGET_VENDOR="none"

 CT_CANADIAN=y

 CT_HOST="i586-mingw32msvc"

 CT_KERNEL_linux=y

 CT_KERNEL_V_2_6_33=y

 CT_BINUTILS_V_2_19_1a=y

 CT_BINUTILS_EXTRA_CONFIG_ARRAY="--enable-targets=i686-none-linux-gnu"

 CT_CC_V_4_3_2=y

 CT_CC_LANG_CXX=y

 CT_LIBC_glibc=y

 CT_LIBC_GLIBC_V_2_9=y

 # CT_LIBC_XLDD is not set

 # CT_LIBC_GLIBC_FORCE_UNWIND is not set

 CT_GMP_V_4_3_2=y

 CT_MPFR_V_2_4_1=y