Our intptr_t and uintptr_t aren't "long". Add a compilation test so we remember
to fix this to cope with 32- and 64-bit later.
Bug: http://code.google.com/p/android/issues/detail?id=57218
Change-Id: I2f816d339edb4f7d57e4418b818fb4c602093f38
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
