match openbsd as well in landmine_utils and breakpad

BUG=

R=thestig@chromium.org

Review URL: https://codereview.chromium.org/760643002

Cr-Commit-Position: refs/heads/master@{#305686}


CrOS-Libchrome-Original-Commit: ea1593d0862064d4ee3818abac68dc84579e346e
diff --git a/build/landmine_utils.py b/build/landmine_utils.py
index 9b667d0..6d18b6d 100644
--- a/build/landmine_utils.py
+++ b/build/landmine_utils.py
@@ -33,7 +33,7 @@
 
 @memoize()
 def IsLinux():
-  return sys.platform.startswith(('linux', 'freebsd'))
+  return sys.platform.startswith(('linux', 'freebsd', 'openbsd'))
 
 
 @memoize()