Changes to compile signing tools on darwin

The following works from a Mac with these changes:
make Q= ARCH=arm HAVE_MACOS=1 `pwd`/build/futility/futility

Only vbutil_keyblock and vbutil_kernel have been exercised.

BUG=none
TEST='make Q= ARCH=arm HAVE_MACOS=1 `pwd`/build/futility/futility'
BRANCH=none

Signed-off-by: David Riley <davidriley@chromium.org>

Change-Id: Ie69cfee0c650d4ff96be6322083a2fea1543ee39
Reviewed-on: https://chromium-review.googlesource.com/246773
Reviewed-by: Bill Richardson <wfrichar@chromium.org>
Tested-by: David Riley <davidriley@chromium.org>
Commit-Queue: David Riley <davidriley@chromium.org>
diff --git a/Makefile b/Makefile
index 2488203..12a27c7 100644
--- a/Makefile
+++ b/Makefile
@@ -179,6 +179,10 @@
   COV_INFO = ${BUILD}/coverage.info
 endif
 
+ifdef HAVE_MACOS
+  CFLAGS += -DHAVE_MACOS -Wno-deprecated-declarations
+endif
+
 # And a few more default utilities
 LD = ${CC}
 CXX ?= g++