Solve more "-finstrument-functions" problems

Solve more "-finstrument-functions" problems (see issue #530).

Our build.mk compiles the independent decompressing executable with
the regular CXXFLAGS, including "-finstrument-functions" if it includes
that - which won't work without the instrumentation functions.

So add "-fno-instrument-functions" when compiling the decompresser.

Signed-off-by: Nadav Har'El <nyh@cloudius-systems.com>
Signed-off-by: Avi Kivity <avi@cloudius-systems.com>