Pass CXXFLAGS to binutils/gold.

The GOLD linker is written in C++. Pass CT_CFLAGS_FOR_HOST as
CXXFLAGS to configure so that any host specific flags are passed
through.

It feels a bit funny passing CFLAGS as CXXFLAGS, but the PPL and GCC
target rules already do the same.

Signed-off-by: Michael Hope <michael.hope@linaro.org>

--- 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