Use SHA1 to verify libbcc is consistent with cache

Modify Android.mk to build a host version of sha1sum.
Modify bcc and MCCacheReader/Writer to check for sha1 on runtime.

Change-Id: I0aa32e2efd85e21f67cd46a20a9e55a430c41f30
diff --git a/lib/ExecutionEngine/MCCacheReader.cpp b/lib/ExecutionEngine/MCCacheReader.cpp
index 35a006a..aac7be7 100644
--- a/lib/ExecutionEngine/MCCacheReader.cpp
+++ b/lib/ExecutionEngine/MCCacheReader.cpp
@@ -151,10 +151,10 @@
     return false;
   }
 
-  if (memcmp(mpHeader->libbcc_build_time, libbcc_build_time, 24) != 0) {
-    mpHeader->libbcc_build_time[24 - 1] = '\0'; // ensure terminated
-    LOGW("Build time mismatch: lib %s cached %s\n", libbcc_build_time,
-         mpHeader->libbcc_build_time);
+  if (memcmp(mpHeader->libbcc_build_checksum, libbcc_build_checksum, 41) != 0) {
+    mpHeader->libbcc_build_checksum[41 - 1] = '\0'; // ensure terminated
+    LOGW("Build checksum mismatch: lib %s cached %s\n", libbcc_build_checksum,
+         mpHeader->libbcc_build_checksum);
     return false;
   }