Build libcares.so on Android.

Adds ares_config.h (derived from ares_config.h.in) and Android.mk. Also,
some small fixes to make the code build without errors:

 ares_build.h: CARES_SIZEOF_LONG defaults to sizeof(long) if no other
 case applies; while this seems to defeat the purpose of defining
 a macro, it works.

 ares_nowarn.c: If HAVE_LIMITS_H is defined, include limits.h and use
 INT_MAX and UINT_MAX as needed.

Bug: 22545809
Change-Id: I628ce2659f6503a415d06db3e223d9ef00956ddb
4 files changed