Fix libweave build issue on Mac builders

libchromeos (which libweave depends on) is not being built on Mac
builders and libweave fails to build because of missing dependencies.

Disable compiling libweave on Mac until libchromeos is fixed

BUG:22948980
Change-Id: I38db08f7494ad176f973b572c0d97e6ca419b81b

libweave/Android.mk

diff --git a/libweave/Android.mk b/libweave/Android.mk
index 932a340..730ba23 100644
--- a/libweave/Android.mk
+++ b/libweave/Android.mk
@@ -14,6 +14,10 @@
 
 LOCAL_PATH := $(call my-dir)
 
+# TODO(avakulenko): Remove this condition when libchromeos can be built on
+# non-Linux host.
+ifeq ($(HOST_OS),linux)
+
 # Common variables
 # ========================================================
 
@@ -211,3 +215,5 @@
 	src/weave_testrunner.cc \
 
 include $(BUILD_NATIVE_TEST)
+
+endif # HOST_OS == linux