Clean up the architecture-specific makefiles.

Group things appropriately and name each group.

Bug: 18160821

(cherry picked from commit 7c02d9428ca18ac600f7ba7d51bb24ca71e733f6)

Change-Id: I863242515af44058154d03e2d8c34678e682d66a
diff --git a/libc/Android.mk b/libc/Android.mk
index 92ead26..61bdf7e 100644
--- a/libc/Android.mk
+++ b/libc/Android.mk
@@ -692,6 +692,7 @@
 LOCAL_SYSTEM_SHARED_LIBRARIES :=
 
 $(eval $(call patch-up-arch-specific-flags,LOCAL_CFLAGS,libc_common_cflags))
+$(eval $(call patch-up-arch-specific-flags,LOCAL_SRC_FILES,libc_freebsd_src_files))
 include $(BUILD_STATIC_LIBRARY)
 
 
@@ -760,6 +761,7 @@
 LOCAL_SYSTEM_SHARED_LIBRARIES :=
 
 $(eval $(call patch-up-arch-specific-flags,LOCAL_CFLAGS,libc_common_cflags))
+$(eval $(call patch-up-arch-specific-flags,LOCAL_SRC_FILES,libc_openbsd_src_files))
 include $(BUILD_STATIC_LIBRARY)