[asan] no ucontext on Android. patch by eugeni.stepanov@gmail.com
[asan] no ucontext on Android. patch by eugeni.stepanov@gmail.com

git-svn-id: c199f293c43da69278bea8e88f92242bf3aa95f7@147320 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