illumos gate

We build an ld to run on the build host to make it easier to use new features in the build. To do this, we try to reuse the normal Makefiles from cmd/sgs. The libld Makefile.com in cmd/sgs/libld ends up adding search paths to the build directories of various cmd/sgs components. When doing a full build, this ends up being fine because there's nothing there and the tools search paths which come later are fine. However, when doing an incremental build, it will actually find and link against these first, which can be especially problematic if they require features from the proto area that aren't on the build system. The solution to this is to just fix up the library paths in the tools Makefile and make sure we don't pick up anything there.