Bug 1083279 - Part 1: Don't get_binary_path on mobile/android. r=gbrown

The logic was cribbed from the final output of |mach run|.

layout/tools/reftest/runreftest.py

@@ -621,7 +621,6 @@ class ReftestOptions(OptionParser):
 
     self.add_option("--appname",
                     action = "store", type = "string", dest = "app",
-                    default = build_obj.get_binary_path() if build_obj else None,
                     help = "absolute path to application, overriding default")
     self.add_option("--extra-profile-file",
                     action = "append", dest = "extraProfileFiles",
@@ -642,7 +641,6 @@ class ReftestOptions(OptionParser):
                     action = "store", type = "string", dest = "utilityPath",
                     help = "absolute path to directory containing utility "
                            "programs (xpcshell, ssltunnel, certutil)")
-    defaults["utilityPath"] = build_obj.bindir if build_obj else None
 
     self.add_option("--total-chunks",
                     type = "int", dest = "totalChunks",
@@ -724,6 +722,14 @@ class ReftestOptions(OptionParser):
                     dest = "extraPrefs", metavar = "PREF=VALUE",
                     help = "defines an extra user preference")
 
+
+    # Certain paths do not make sense when we're cross compiling Fennec.  This
+    # logic is cribbed from the example in
+    # python/mozbuild/mozbuild/mach_commands.py.
+    if build_obj and build_obj.substs['MOZ_BUILD_APP'] != 'mobile/android':
+        defaults['appname'] = build_obj.get_binary_path() if build_obj else None
+        defaults["utilityPath"] = build_obj.bindir if build_obj else None
+
     self.set_defaults(**defaults)
 
   def verifyCommonOptions(self, options, reftest):