fbcode_builder: getdeps: add platform type tuple helper

Summary:
This will feed into the manifest context for system
dependent manifest sections.  This is essentially the same
code borrowed from the watchman and eden getdeps.py.

Reviewed By: simpkins

Differential Revision: D14690997

fbshipit-source-id: 3d3ae146237a2cd49609aaa2bd0e785ebe21f02c

build/fbcode_builder/getdeps.py

@@ -15,6 +15,7 @@ import subprocess
 import sys
 
 from getdeps.manifest import ManifestParser
+from getdeps.platform import HostType
 from getdeps.subcmd import SubCmd, add_subcommands, cmd
 
 
@@ -36,6 +37,14 @@ class ValidateManifest(SubCmd):
         parser.add_argument("file_name", help="path to the manifest file")
 
 
+@cmd("show-host-type", "outputs the host type tuple for the host machine")
+class ShowHostType(SubCmd):
+    def run(self, args):
+        host = HostType()
+        print("%s" % host.as_tuple_string())
+        return 0
+
+
 def build_argparser():
     ap = argparse.ArgumentParser(description="Get and build dependencies and projects")
     sub = ap.add_subparsers(