This also allows us to optimize the case where we increment an
uncontended semaphore (no need to call futex_wake() then).
Change-Id: Iad48efe8551dc66dc89d3e3f18c001e5a6c1939f
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