Add bionic support to endian.h

Bionic supports byteswap. Protobuf will support bionic in the near future,
which leads to macro-redefinition errors. Add recognition of bionic.

Bug: 72746797
Test: mmma external/libtextclassifier
Merged-In: I65cb7f0b067b68e3e1c22ee87232555887446089
Change-Id: I7fd9a1335a4b6cac51ab8e183d71a4e21ac59fee