[v0.3.1-0.3.5]builds fail with "can't find crate for `core`"

[taro-k]

I tried to build from 0.3.1 to 0.3.5 but always end up with the error like following. The situation is same for gradlew build. Please help if any idea. thx

./gradlew assembleArm

> Task :buildArmBinary FAILED
+ cargo test
    Finished dev [unoptimized + debuginfo] target(s) in 0.02s
     Running target/debug/deps/oab_utils-0cfc108789716157

running 8 tests
test test_main::test_parse_id_input ... ok
test test_main::test_parse_id_input_only_uid ... ok
test test_main::test_get_owner_ids ... ok
test test_main::test_parse_id_input_parse_groupname ... ok
test test_main::test_parse_id_input_parse_username ... ok
test test_main::test_parse_id_input_error ... ok
test test_main::test_parse_id_input_username_groupname ... ok
test test_main::test_get_owner_ids_no_such_file ... ok

test result: ok. 8 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

+ cargo build --release --target armv7-linux-androideabi
   Compiling libc v0.2.40
   Compiling unicode-width v0.1.4
   Compiling ansi_term v0.11.0
   Compiling vec_map v0.8.1
error[E0463]: can't find crate for `core`
  |
  = note: the `armv7-linux-androideabi` target may not be installed

error: aborting due to previous error

error: Could not compile `unicode-width`.
warning: build failed, waiting for other jobs to finish...
error[E0463]: can't find crate for `core`
  |
  = note: the `armv7-linux-androideabi` target may not be installed

error: aborting due to previous error

error: Could not compile `bitflags`.
warning: build failed, waiting for other jobs to finish...
error[E0463]: can't find crate for `std`
  |
  = note: the `armv7-linux-androideabi` target may not be installed

error: aborting due to previous error

...

[jensstein]

you don't seem to have the needed toolchain installed. try running rustup target add armv7-linux-androideabi. you can find detailed steps for building in the file .gitlab-ci.yml