You receive this bug because this package does not respect my system's CXX ( x86_64-pc-linux-gnu-g++ - /usr/bin/x86_64-pc-linux-gnu-g++ ) and calls directly g++ -/usr/bin/g++ 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)" There are few files compiled with c++. grep "^c++" $log to check. c++ -o host_jskwgen.o -c -march=native -pipe -Wno-return-type -w -mno-avx -I/usr/lib64/libffi-3.0.11/include -I. -I/var/tmp/portage/mail-client/thunderbird-17.0.4/work/comm-esr17/mozilla/js/src/../../mfbt/double-conversion -I/var/tmp/portage/mail-client/thunderbird-17.0.4/work/comm-esr17/mozilla/js/src -I. -I./../../dist/include -I/usr/include/nspr -I/var/tmp/portage/mail-client/thunderbird-17.0.4/work/comm-esr17/mozilla/js/src -I/var/tmp/portage/mail-client/thunderbird-17.0.4/work/comm-esr17/mozilla/js/src/assembler -I/var/tmp/portage/mail-client/thunderbird-17.0.4/work/comm-esr17/mozilla/js/src/yarr -I/usr/include/nspr /var/tmp/portage/mail-client/thunderbird-17.0.4/work/comm-esr17/mozilla/js/src/jskwgen.cpp
If you are still seeing this please reopen.