add(sys-devel/sysroot-wrappers): Add new sysroot-wrappers tool.

This replaces the previous sysroot wrapper scripts that was bundled with
the Google toolchain. This one is implemented in a more generic manner
and based on ccache. Perhaps other custom wrapper scripts will
eventually move into this package as well.
Merge pull request #82 from marineam/wrappers

add(sys-devel/sysroot-wrappers): Add new sysroot-wrappers tool.