kbuild: simplify silent build (-s) detection

This allows to detect -s (--silent) option without checking GNU Make
version.

As commit e36aaea2 ("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 e6ac89fa ("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: NMasahiro Yamada <yamada.masahiro@socionext.com>

Makefile

@@ -84,17 +84,10 @@ endif
 # If the user is running make -s (silent mode), suppress echoing of
 # commands
 
-ifneq ($(filter 4.%,$(MAKE_VERSION)),)	# make-4
-ifneq ($(filter %s ,$(firstword x$(MAKEFLAGS))),)
+ifneq ($(findstring s,$(filter-out --%,$(MAKEFLAGS))),)
   quiet=silent_
   tools_silent=s
 endif
-else					# make-3.8x
-ifneq ($(filter s% -s%,$(MAKEFLAGS)),)
-  quiet=silent_
-  tools_silent=-s
-endif
-endif
 
 export quiet Q KBUILD_VERBOSE
 

tools/build/Makefile.build

@@ -19,15 +19,9 @@ else
   Q=@
 endif
 
-ifneq ($(filter 4.%,$(MAKE_VERSION)),)	# make-4
-ifneq ($(filter %s ,$(firstword x$(MAKEFLAGS))),)
+ifneq ($(findstring s,$(filter-out --%,$(MAKEFLAGS))),)
   quiet=silent_
 endif
-else					# make-3.8x
-ifneq ($(filter s% -s%,$(MAKEFLAGS)),)
-  quiet=silent_
-endif
-endif
 
 build-dir := $(srctree)/tools/build
 

tools/scripts/Makefile.include

@@ -58,15 +58,9 @@ else
 NO_SUBDIR = :
 endif
 
-ifneq ($(filter 4.%,$(MAKE_VERSION)),)  # make-4
-ifneq ($(filter %s ,$(firstword x$(MAKEFLAGS))),)
+ifneq ($(findstring s,$(filter-out --%,$(MAKEFLAGS))),)
   silent=1
 endif
-else					# make-3.8x
-ifneq ($(filter s% -s%,$(MAKEFLAGS)),)
-  silent=1
-endif
-endif
 
 #
 # Define a callable command for descending to a new directory