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

 --- gcc-4.3.4/libffi/src/arm/sysv.S	

 +++ gcc-4.3.4/libffi/src/arm/sysv.S	

 @@ -235,7 +235,7 @@ ARM_FUNC_START ffi_closure_SYSV

  	stmfd	sp!, {ip, lr}

  	UNWIND .save	{r0, lr}

  	add	r2, sp, #8

 -	.pad #16

 +	UNWIND .pad #16

  	sub	sp, sp, #16

  	str	sp, [sp, #8]

  	add	r1, sp, #8