[gm.py] Fix Python2 compatibility

The recent arm64 improvements unintentionally required Python3.

No-Try: true
Change-Id: Ide94ea99cb69c530b3896e6577bd0b536e5374c9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2754407Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Auto-Submit: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73365}

tools/dev/gm.py

@@ -214,6 +214,11 @@ def _Notify(summary, body):
   else:
     print("{} - {}".format(summary, body))
 
+def _GetMachine():
+  # Once we migrate to Python3, this can use os.uname().machine.
+  # The index-based access is compatible with all Python versions.
+  return os.uname()[4]
+
 def GetPath(arch, mode):
   subdir = "%s.%s" % (arch, mode)
   return os.path.join(OUTDIR, subdir)
@@ -246,10 +251,10 @@ class Config(object):
       cpu = "arm"
     elif self.arch == "android_arm64":
       cpu = "arm64"
-    elif self.arch == "arm64" and os.uname().machine == "aarch64":
+    elif self.arch == "arm64" and _GetMachine() == "aarch64":
       # arm64 build host:
       cpu = "arm64"
-    elif self.arch == "arm" and os.uname().machine == "aarch64":
+    elif self.arch == "arm" and _GetMachine() == "aarch64":
       cpu = "arm"
     elif "64" in self.arch or self.arch == "s390x":
       # Native x64 or simulator build.
@@ -274,7 +279,7 @@ class Config(object):
     return []
 
   def GetSpecialCompiler(self):
-    if os.uname().machine == "aarch64":
+    if _GetMachine() == "aarch64":
       # We have no prebuilt Clang for arm64. Use the system Clang instead.
       return ["clang_base_path = \"/usr\"", "clang_use_chrome_plugins = false"]
     return []