compiling some source here

I'm compiling some software for which a port is not available. If I can make the thing to compile and run, many FreeBSD users would be very happy. It looks like I've satisfied some prerequisites for it, so now it's compiling further. Here's what I bumped into now and web search doesn't seem to help. You guys here are very smart, so if you would be so kind please help:
c++: error: unknown argument: '-fno-tree-vrp'
using devel/gmake and lang/gcc (which currently is at 4.8.5_2)
You're very light on the details... Which software is this? What build system does it use? How are you making sure it's using gcc?

c++: error: unknown argument: '-fno-tree-vrp'
It's using the system compiler c++ for something, not g++ as you probably intended.
Usually you have to use the following environment to force a certain compiler to be used, for example if you want to force /usr/local/bin/gcc48 to be used all around in the compilation instead of system cc(1):

env CC=gcc48 CXX=g++48 CPP="gcc48 -E" make ...
Thanks for your timely replies. The source is intended to compile on Linux. Don't worry about the error above anymore, I deleted gcc and installed clang instead, now it's going strong for a while way past the above error spot.

I have another question. There is a configure parameter that I need to pass. I figured that the following works:
gmake CONFIGURE_ARGS+=--disable-some-crap
Is this how the proper way to pass such arguments?
the documentation calls explicitly against clang, so I'm back to gcc now. Kpa's suggestion got me past the original error. Here's what I'm facing now:
g++: error: unrecognized command line option '-Qunused-arguments'
Would appreciate any help with it