maint: address sc_prohibit_always-defined_macros.

* cfg.mk: No longer skip it, except where EXIT_SUCCESS is used
	as a witness for stdlib.h.
	Skip this test when appropriate.
	* data/yacc.c: Drop a note about why EXIT_SUCCESS is defined here.

cfg.mk

@@ -35,7 +35,6 @@ url_dir_list = \
 # Tests not to run as part of "make distcheck".
 local-checks-to-skip =			\
   sc_immutable_NEWS			\
-  sc_prohibit_always-defined_macros	\
   sc_prohibit_always_true_header_tests	\
   sc_prohibit_atoi_atof			\
   sc_prohibit_doubled_word		\
@@ -56,11 +55,14 @@ update-copyright-env = \
   UPDATE_COPYRIGHT_FORCE=1 UPDATE_COPYRIGHT_USE_INTERVALS=1
 
 exclude = $(foreach a,$(1),$(eval exclude_file_name_regexp--sc_$(a)))
-$(call exclude,							\
-  bindtextdomain=^lib/main.c$$					\
-  program_name=^lib/main.c$$					\
-  prohibit_empty_lines_at_EOF=^src/parse-gram.h$$		\
-  require_config_h_first=^(lib/yyerror|data/(glr|yacc))\.c$$	\
-  space_tab=^tests/(input|c\+\+)\.at$$				\
-  unmarked_diagnostics=^djgpp/					\
+$(call exclude,								\
+  bindtextdomain=^lib/main.c$$						\
+  program_name=^lib/main.c$$						\
+  prohibit_always-defined_macros=^data/yacc.c|^djgpp/			\
+  prohibit_always-defined_macros+=?|^src/(parse-gram.c|system.h)$$	\
+  prohibit_always-defined_macros+=?|^tests/regression.at$$		\
+  prohibit_empty_lines_at_EOF=^src/parse-gram.h$$			\
+  require_config_h_first=^(lib/yyerror|data/(glr|yacc))\.c$$		\
+  space_tab=^tests/(input|c\+\+)\.at$$					\
+  unmarked_diagnostics=^djgpp/						\
 )