Pass the path to the program to scripts/check_sparse.py, which
previously was not included in config-host.mak.  Change
scripts/check_sparse.py to work with cgcc, which seems to
work better with sparse 0.6.x.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Do not use cgcc; instead, extract compilation commands from compile_commands.json
and invoke sparse directly.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>