Speeding up make by 4 seconds :)

I found a way to reduce the amount of processing GNU make does when
building with the LLVM Makefile system: "make -r". We don't need or use
any of the built-in rules that make has. The -r option omits them. This
means make will perform many thousand fewer (and unnecessary) tests.
When I did:

make ; time make ; time make -r

You should get something like:

real 0m6.484s
user 0m4.787s
sys 0m1.661s

make -r:
real 0m2.896s
user 0m1.803s
sys 0m0.856s

This shaves a few seconds off the makefile processing. This might help
out a bit on slower machines.