check-recipe: generalize dependency control

An initial (and quite naive) implementation was done
for conf.d/ files but features do need it as well --
which became obvious during a casual inspection of
distro/alt-workstation's target graph (which occured
broken).

The code is a messy hackery unfortunately, regexes used
are fragile regarding e.g. [A-Z_] in target names.
Read with care.

NB: lib/ might need this too but it's rather stable
    and contains some special cases that would obstruct
    the regexes even more...

bin/check-recipe

@@ -0,0 +1,14 @@
+#!/bin/sh
+
+# missing "; @:" for recipeless rules makes SHELL payload useless
+# (see also ../lib/report.mk); this results in broken target graphs
+# (so REPORT=1 gets crippled)
+
+  sed 's/^[a-z]\+\/.*:.*$/\n&/' "$@" \
+| grep -vE '^(#|export|if|else|endif|define|endef)' \
+| sed ':loop /^[^#].*[^\\]\\$/N; s/\\\n//; t loop' \
+| grep -vE ':=| = | ?= | += |^\$' \
+| sed ':loop /^[a-z]\+\/.*:.*$/N; s/\n\t\+@*/\; /; t loop' \
+| grep -vE ';|^$' && exit 1 ||:
+
+# see also http://unix.stackexchange.com/questions/228547

conf.d/Makefile

@@ -1,5 +1,2 @@
-# missing "; @:" for recipeless rules makes SHELL payload useless
-# (see also ../lib/report.mk); this results in broken target graphs
-# (so REPORT=1 gets crippled)
 check:
-	@grep -E '^[a-z]+/.*: .*[^\\:]$$' *.mk
+	@../bin/check-recipe *.mk

features.in/Makefile

@@ -25,6 +25,9 @@ define grepper_body
 	done
 endef
 
+check:
+	@../bin/check-recipe */config.mk
+
 %:
 	$(error BUILDDIR not defined)