infra/utils: add helper to generate comma-separated lists

Add a helper macro that, from a space-separated list of items, returns a
comma-separated list of the quoted items.

This will be useful when we need to generate lists in JSON, later...

Code suggested by Thomas P.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas De Schampheleire <patrickdepinguin@gmail.com>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Cc: Arnout Vandecappelle <arnout@mind.be>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

support/misc/utils.mk

@@ -70,6 +70,10 @@ finddirclauses = $(call notfirstword,$(patsubst %,-o -path '$(1)/%',$(2)))
 # notfirstword(wordlist): returns all but the first word in wordlist
 notfirstword = $(wordlist 2,$(words $(1)),$(1))
 
+# build a comma-separated list of quoted items, from a space-separated
+# list of unquoted items:   a b c d  -->  "a", "b", "c", "d"
+make-comma-list = $(subst $(space),$(comma)$(space),$(patsubst %,"%",$(strip $(1))))
+
 # Needed for the foreach loops to loop over the list of hooks, so that
 # each hook call is properly separated by a newline.
 define sep