On BSDs "make" is typically BSD make, while "gmake" is GNU make.

Signed-off-by: Ed Maste <emaste@freebsd.org>
Message-Id: <1427911118-21905-1-git-send-email-emaste@freebsd.org>
[Fix $(INSTALLER) too as reported by Fam Zheng. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>