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/CacheWriter.cpp b/lib/ExecutionEngine/CacheWriter.cpp
index 67def9b..ab8dd03 100644
--- a/lib/ExecutionEngine/CacheWriter.cpp
+++ b/lib/ExecutionEngine/CacheWriter.cpp
@@ -93,7 +93,7 @@
   // Magic word and version
   memcpy(header->magic, OBCC_MAGIC, 4);
   memcpy(header->version, OBCC_VERSION, 4);
-  memcpy(header->libbcc_build_time, libbcc_build_time, 24);
+  memcpy(header->libbcc_build_checksum, libbcc_build_checksum, 41);
 
   // Machine Integer Type
   uint32_t number = 0x00000001;