libc/newlib: fix host/target confusion

newlib handles the build/host/target a bit differently as one would expect:
build : not used
host : the nachine that builds newlib
target : the machine on which newlib will run

 reporter_name="Ioannis E. VENETIS"

 reporter_url="http://sourceware.org/ml/crossgcc/2008-06/msg00017.html"

 reporter_comment=""