do not touch any resources.
*   `tf.cond`, `tf.while` and `if` and `while` in AutoGraph now accept a
    nonscalar predicate if has a single element. This does not affect non-V2
    control flow.
*   `tf.while_loop` emits a StatelessWhile op if the cond and body functions are
    stateless and do not touch any resources.

build:macos --define=PREFIX=/usr
build:macos --define=LIBDIR=$(PREFIX)/lib
build:macos --define=INCLUDEDIR=$(PREFIX)/include
build:macos --define=PROTOBUF_INCLUDE_PATH=$(PREFIX)/include
# TF_SYSTEM_LIBS do not work on windows.

# By default, build TF in C++ 17 mode.
build:android --cxxopt=-std=c++17
build:android --host_cxxopt=-std=c++17
build:ios --cxxopt=-std=c++17
build:ios --host_cxxopt=-std=c++17