* Added a few header files in headers/posix/arch that'll allow for an x86_64
haiku target to be compiled. fenv.h is src/lib/msun/amd64/fenv.h from
freebsd.
* configure: Added support for x86_64 arch when running
build_cross_tools_gcc4.
* config[_build]/HaikuConfig.h, BuildSetup: Added x86_64 recognition.
git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@36794 a95241bf-73f2-0310-859d-f6bbb57e9c96
