Add a new header that defines __ANDROID_API__ as a constant integer
corresponding to the current native API level. This header is included
by <sys/cdefs.h>
Change-Id: Ib4774e247b395991266245815a24292afc919848
NOTE: This header is already provided by the NDK's platform headers.
for levels 3 to 9.
Also add missing declarations to misc. functions.
Fix clearerr() implementation (previous was broken).
Handle feature test macros like _POSIX_C_SOURCE properly.
Change-Id: Icdc973a6b9d550a166fc2545f727ea837fe800c4
