Break debugger on assertion failure. This adds a few simple system utility functions. We can check if a debugger is attached and break into the debugger. Most of the code is adapted from Chromium's base/debug. Bug: angleproject:3162 Change-Id: I9cb39d42865a543fbf3201222dd8227318b32ad5 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1615353 Reviewed-by: Jonah Ryan-Davis <jonahr@google.com> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>