Support composite images.

This adds a --composite_disk flag to launch_cvd which optionally uses a
composite disk image for all the partitions. If the file does not
already exist, it is assembled on-demand using bpttool.

Only implemented in crosvm for now.

Bug: 133432409
Change-Id: I135513ba03331472a13241c49506fc1b5869a6e0
Test: launch_cvd -vm_manager=crosvm
Test: launch_cvd -vm_manager=crosvm --composite_disk=composite.img
diff --git a/Android.bp b/Android.bp
index 624154c..54084f1 100644
--- a/Android.bp
+++ b/Android.bp
@@ -68,7 +68,7 @@
             enabled: false,
         },
     },
-    cflags: ["-Werror", "-Wall"],
+    cflags: ["-Werror", "-Wall", "-D_FILE_OFFSET_BITS=64"],
     vendor: true,
 }