Backed out changeset b541ce3cbff5 (bug 1277087) for ab build failures

--HG--
extra : rebase_source : bad752021d110e22a4942fd23a9ec04c780a677c

build/mach_bootstrap.py

@@ -233,8 +233,11 @@ def bootstrap(topsrcdir, mozilla_dir=None):
     # case. For default behavior, we educate users and give them an opportunity
     # to react. We always exit after creating the directory because users don't
     # like surprises.
-    sys.path[0:0] = [os.path.join(mozilla_dir, path) for path in SEARCH_PATHS]
-    import mach.main
+    try:
+        import mach.main
+    except ImportError:
+        sys.path[0:0] = [os.path.join(mozilla_dir, path) for path in SEARCH_PATHS]
+        import mach.main
 
     def telemetry_handler(context, data):
         # We have not opted-in to telemetry