Build unittests on Android.

The unitests were compiled in the Makefile but not on Android. This
patch builds the unittests for the host on Android.

Bug: 24478450
Test: mmma external/bsdiff && out/host/linux-x86/bin/bsdiff_unittest

Change-Id: Ib9f70e57273e585f31b46068d29b277aaae611eb
diff --git a/bsdiff_unittest.cc b/bsdiff_unittest.cc
index 54361a7..b3aae3e 100644
--- a/bsdiff_unittest.cc
+++ b/bsdiff_unittest.cc
@@ -42,7 +42,7 @@
 
   // An empty bz2 file will have 14 bytes.
   EXPECT_EQ(14, patch.diff_len);
-  EXPECT_EQ(14, patch.extra_len);
+  EXPECT_EQ(14U, patch.extra_len);
 }
 
 TEST_F(BsdiffTest, EqualSmallFiles) {
@@ -58,7 +58,7 @@
 
   // An empty bz2 file will have 14 bytes.
   EXPECT_EQ(14, patch.diff_len);
-  EXPECT_EQ(14, patch.extra_len);
+  EXPECT_EQ(14U, patch.extra_len);
 }
 
 }  // namespace bsdiff