[PATCH v2] kbuild: simplify silent build (-s) detection

This allows to detect -s (--silent) option without checking GNU Make version. As commit e36aaea28972 ("kbuild: Fix silent builds with make-4") pointed out, GNU Make 4.x changed the way/order it presents the command line options into MAKEFLAGS. In Make 3.8x, 's' is always be the first in a group

[PATCH v2] kbuild: simplify silent build (-s) detection

This allows to detect -s (--silent) option without checking GNU Make version. As commit e36aaea28972 ("kbuild: Fix silent builds with make-4") pointed out, GNU Make 4.x changed the way/order it presents the command line options into MAKEFLAGS. In Make 3.8x, 's' is always be the first in a group