Emit unique linker buildid in all binaries.

We want to store the symbol information for all android binaries in a global database.

* We ingest unstripped binaries into the global database
* When we collect address data from device (e.g. instruction pointer address), we want to lookup its symbol information through the global database. The key of the mapping is a unique build id, which is the same between binaries on device (stripped) and unstripped binaries.

After applying this patch, the system.img size increases by 0.0047% (16.3KB).

Change-Id: Id92faf2951f43a30947e8d2b690c1af6bf7e3f54
diff --git a/core/combo/TARGET_linux-x86.mk b/core/combo/TARGET_linux-x86.mk
index c2188c0..e22500e 100644
--- a/core/combo/TARGET_linux-x86.mk
+++ b/core/combo/TARGET_linux-x86.mk
@@ -122,6 +122,7 @@
 
 $(combo_2nd_arch_prefix)TARGET_GLOBAL_LDFLAGS += -Wl,-z,noexecstack
 $(combo_2nd_arch_prefix)TARGET_GLOBAL_LDFLAGS += -Wl,-z,relro -Wl,-z,now
+$(combo_2nd_arch_prefix)TARGET_GLOBAL_LDFLAGS += -Wl,--build-id=md5
 $(combo_2nd_arch_prefix)TARGET_GLOBAL_LDFLAGS += -Wl,--warn-shared-textrel
 $(combo_2nd_arch_prefix)TARGET_GLOBAL_LDFLAGS += -Wl,--fatal-warnings
 $(combo_2nd_arch_prefix)TARGET_GLOBAL_LDFLAGS += -Wl,--gc-sections