seccomp-x86: allow sched_yield and gettid syscalls

Addresses:
media.extractor: libminijail: blocked syscall: sched_yield, gettid

Bug: None
Test: make USE_CLANG_PLATFORM_BUILD:=true SANITIZE_TARGET=address -j42
      media extractor complains no more.
Change-Id: I3d499b0400df10ede08801fe6b608e6003727734