support _POSIX_CPUTIME

Bug: 18490039
Change-Id: I01fa83b48e1b908de1f227b6e4f98e280bcd50ee
libc: Fix headers to allow direct inclusion.

These headers are missing a few #includes to allow their direct
inclusion from C

http://b.android.com/79841

Change-Id: Ifc712c17f4da70b26adb67d4d49ed659f53c3621
Merge "libc: Fix headers to allow direct inclusion."
Merge "support _POSIX_CPUTIME"