goma_link: add phony rules for native object files

crrev.com/c/2271896 changed the ninja files that are generated by
goma_link to build .o.stamp files for native object files, instead
of .o files directly. The present change adds phony rules with the
.o name, so that you can use ninja foo.o to build foo.o, instead
of having to write ninja foo.o.stamp.

Bug: 1072888
Change-Id: I14d5f33a1b1ccc6677e58fb6efa4c8a02981e9de
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2274864
Commit-Queue: Bob Haarman <inglorion@chromium.org>
Reviewed-by: George Burgess <gbiv@chromium.org>
Cr-Commit-Position: refs/heads/master@{#784174}

tools/clang/scripts/goma_link.py

@@ -596,13 +596,15 @@ class GomaLinkBase(object):
       for tup in params.codegen:
         obj, bitcode, index = tup
         stamp = obj + '.stamp'
-        native_link_deps.append(stamp)
+        native_link_deps.append(obj)
         f.write(
             ('\nbuild %s : codegen %s %s\n'
              '  bitcode = %s\n'
              '  index = %s\n'
-             '  native = %s\n') %
-            tuple(map(ninjaenc, (stamp, bitcode, index, bitcode, index, obj))))
+             '  native = %s\n'
+             '\nbuild %s : phony %s\n') % tuple(
+                 map(ninjaenc,
+                     (stamp, bitcode, index, bitcode, index, obj, obj, stamp))))
 
       f.write(('\nbuild %s : native-link %s\n'
                '  rspname = %s\n  params = %s\n') %