native profiling support

only works with Linux for now
change target name, add cachegrind target
rebase_fixup
make: streamline native targets

The new target names are easier to remember / decipher:

term
term-cachegrind
term-gprof
term-valgrind

all
all-cachegrind
all-gprof
all-valgrind
all-debug

eval-gprof
eval-cachegrind
add variables for gprof, cg_annotate
examples/hello-world: return instead of busy loop.
Merge pull request #973 from LudwigOrtmann/examples_hello-world_update

examples/hello-world: return instead of busy loop.
Merge pull request #789 from LudwigOrtmann/native_gprof

native profiling tools support
Merge remote-tracking branch 'riot_readonly/master'