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>

 #!/bin/sh

 tail -n+5 "${0}" |bzcat

 exit 0