[ASan] Move the sigaltstack() bits to sanitizer_common.
This change is a part of refactoring intended to have common signal handling behavior in all tools.
Note that this particular change doesn't enable use_sigaltstack support in every tool.



git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@200310 91177308-0d34-0410-b5e6-96231b3b80d8