我正在尝试执行gem install therubyracer-heroku -v '0.8.1.pre3'，但是在构建时遇到错误，这是一个很大的日志，但这是最后失败的行（最后粘贴了完整的日志）：
g++ -o obj/release/bootstrapper.o -c -Wall -Werror -W -Wno-unused-parameter -Wnon-virtual-dtor -pedantic -m32 -O3 -fomit-frame-pointer -fdata-sections -ffunction-sections -ansi -fno-rtti -fno-exceptions -fvisibility=hidden -Wall -Werror -W -Wno-unused-parameter -Wnon-virtual-dtor -pedantic -m32 -O3 -fomit-frame-pointer -fdata-sections -ffunction-sections -ansi -DV8_TARGET_ARCH_IA32 -DENABLE_VMSTATE_TRACKING -DENABLE_LOGGING_AND_PROFILING -DENABLE_DEBUGGER_SUPPORT -Isrc src/bootstrapper.cc
src/bootstrapper.cc: In static member function 'static bool v8::internal::Genesis::CompileScriptCached(v8::internal::Vector<const char>, v8::internal::Handle<v8::internal::String>, v8::internal::SourceCodeCache*, v8::Extension*, v8::internal::Handle<v8::internal::Context>, bool)':
src/bootstrapper.cc:1002:18: error: variable 'result' set but not used [-Werror=unused-but-set-variable]
src/bootstrapper.cc: In member function 'bool v8::internal::Genesis::InstallNatives()':
src/bootstrapper.cc:1227:24: error: variable 'name' set but not used [-Werror=unused-but-set-variable]
cc1plus: all warnings being treated as errors
scons: *** [obj/release/bootstrapper.o] Error 1
scons: building terminated because of errors.
make: *** [build/v8/libv8.a] Error 2
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of
necessary libraries and/or headers. Check the mkmf.log file for more
details. You may need configuration options.
我已经在谷歌上搜索了很多小时，并研究了很多类似的问题，但没有任何帮助，我也不知道 mkmf log 的含义是什么以及在哪里可以找到它。
附加信息：
OS: Ubuntu, 12.04
I already have nodeJs installed, version is v0.8.14 (Just giving this info, since it may be linked with this)
Ruby version: 1.9.3
RVM is used