[ASan] Add allow_user_segv_handler to let users override SEGV handler installed by ASan

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@180255 91177308-0d34-0410-b5e6-96231b3b80d8
Add -fno-rtti to ASan runtime cflags on Android.

Otherwise we are picking up an extra libstdc++ dependency.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@180265 91177308-0d34-0410-b5e6-96231b3b80d8