You receive this bug because this package does not respect my system's CXX (x86_64-pc-linux-gnu-g++) and calls directly /usr/bin/g++(or similar)
The possible solutions to fix this issue are:
1)Fix the buildsystem, if you can;
2)inherit toolchain-funcs and use tc-export CXX
3)inherit toolchain-funcs and use emake CXX="$(tc-getCXX)"
From the build log:
checking for g++... g++
It does some tests in the configure phase with g++ instead of $CXX, check the CC stuff too.
I just configured Mesa with CXX=x86_64-pc-linux-gnu-g++-4.8.2 and didn't see any evidence of this.