Compile delta_generator for the host.

Bug: 24619596
TEST=mma on linux.

Change-Id: Icccae2b938b4fdd698b177beee96ffb62e9f63ae
diff --git a/payload_consumer/file_descriptor.cc b/payload_consumer/file_descriptor.cc
index f26be28..309c60d 100644
--- a/payload_consumer/file_descriptor.cc
+++ b/payload_consumer/file_descriptor.cc
@@ -69,6 +69,11 @@
                                        uint64_t start,
                                        uint64_t length,
                                        int* result) {
+  // If the ioctl BLKZEROOUT is not defined, just fail to perform any of these
+  // operations.
+#ifndef BLKZEROOUT
+  return false;
+#else  // defined(BLKZEROOUT)
   DCHECK(request == BLKDISCARD || request == BLKZEROOUT ||
          request == BLKSECDISCARD);
   // On some devices, the BLKDISCARD will actually read back as zeros, instead
@@ -99,6 +104,7 @@
     return false;
   }
   return true;
+#endif  // defined(BLKZEROOUT)
 }
 
 bool EintrSafeFileDescriptor::Close() {