xnu output is now accessible by other targets.
Added libkmodc and libkmodc++.

I also fixed some build issues in the mach_kernel that were preventing these libraries from compiling.
Added libsyscall.
The build now logs into the DERIVED_FILE_DIR.

Previously, when mach_kernel was built, it would log into a file in $(TMPDIR), which is a per-user, non-project-specific variable. This was for my ease of debugging the mach_kernel build. That is unneeded now, so I cleaned up the build slightly.