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/+/1615353Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>