[esan] Fix sideline thread flaky assert
[esan] Fix sideline thread flaky assert

Fixes an esan sideline thread CHECK that failed to account for the sideline
thread reaching its code before the internal_clone() return value was
assigned in the parent.

git-svn-id: c199f293c43da69278bea8e88f92242bf3aa95f7@275946 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt