Add avbtool alias

As a replacement for the removal of the avbtool symlink

Bug: 198619163
Test: Manually running `avbtool`
Change-Id: I54d504a5132e5ac89337e67a07bca0a6f410c272
diff --git a/envsetup.sh b/envsetup.sh
index 550dca8..3f5ce33 100644
--- a/envsetup.sh
+++ b/envsetup.sh
@@ -2045,6 +2045,13 @@
     fi
 }
 
+function avbtool() {
+    if [[ ! -f "$ANDROID_SOONG_HOST_OUT"/bin/avbtool ]]; then
+        m avbtool
+    fi
+    "$ANDROID_SOONG_HOST_OUT"/bin/avbtool $@
+}
+
 validate_current_shell
 source_vendorsetup
 addcompletions