Makefile: Fix regression in .SILENT rule

Since commit d74e651b78 (Makefiles: Re-implement makefile target path
escaping and quoting, 2020-04-10, v3.18.0-rc1~334^2~1), `WriteMakeRule`
now correctly escapes `$` in make target paths as `$$`.  However, this
caused an existing call site to escape the `$(VERBOSE)` variable
reference in the `.SILENT` prefix, making it ineffective.  Sub-makefiles
are invoked with `MAKESILENT`, so this bug matters only for the `all`
target, which emits progress messages from toplevel.


    # Suppress display of executed commands.


    # Suppress display of executed commands.
1 file changed