This allows to detect -s (--silent) option without checking GNU Make
version.
As commit e36aaea289 ("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 the first in a group of short options.
The group may be prefixed with '-' in some cases.
In Make 4.x, 's' is always the last in a group of short options.
As commit e6ac89fabd ("kbuild: Correctly deal with make options
which contain an 's'") addressed, we also need to deal with long
options that contain 's', like --warn-undefined-variables.
Test cases:
[1] command line input: make --silent
-> MAKEFLAGS for Make 3.8x: s
-> MAKEFLAGS for Make 4.x : s
[2] command line input: make -srR
-> MAKEFLAGS for Make 3.8x: sRr
-> MAKEFLAGS for Make 4.x : rRs
[3] command line input: make -s -rR --warn-undefined-variables
-> MAKEFLAGS for Make 3.8x: --warn-undefined-variables -sRr
-> MAKEFLAGS for Make 4.x : rRs --warn-undefined-variables
My idea to cater to all the cases more easily is to filter out long
options (--%), then search 's' with $(findstring ...). This way will
be more future-proof even if future versions of Make put 's' in the
middle of the group.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
6f0fa58e45