Makefiles: Silencing GNU make 4.3 nested invocations
EDIT: See #20487 (comment 718428) for full description.
Per https://savannah.gnu.org/bugs/?54740, gmake 4.3 and later do not apply .SILENT
to recursive make invokations. Currently, we only place it at the top-level, but will need to be put at all levels now.
Edited by Brad King