Use __fake.?__ syntax for fake genrule outputs

These genrules do not produce an output file, instead they are run
by the developer to obtain their side-effects like building other
targets they happen to depend on.

Make it more clear these are fake by naming them __fake.?__, a name
we should never see appear in buck-out/.

Change-Id: Id749b095a0b2990f8d9c7e3942215fc7463a5255
1 file changed