[lsan] Use a more standard-conformant sched_yield() instead of pthread_yield().
There's no pthread_yield() on OSX (only sched_yield() and pthread_yield_np()).


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@213516 91177308-0d34-0410-b5e6-96231b3b80d8
[lsan] Define MAP_ANONYMOUS as MAP_ANON for OSX in the test.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@213518 91177308-0d34-0410-b5e6-96231b3b80d8
[lsan] Allow using ucontext.h in the test on OSX.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@213523 91177308-0d34-0410-b5e6-96231b3b80d8