build: avoid repetition of `LC_ALL=C sort`

Put `LC_ALL=C sort` in a variable and use it everywhere. It was
forgotten in one place.

Without `LC_ALL=C` it would order `a.b` before `a-c` even though
`. (0x2E)` > `- (0x2D)`.

Changelog-None

Makefile

@@ -19,6 +19,8 @@ BOLTVERSION := 17df7f2bba4dab844569c3305201606dee800741
 
 -include config.vars
 
+SORT=LC_ALL=C sort
+
 ifneq ($(VALGRIND),0)
 VG=VALGRIND=1 valgrind -q --error-exitcode=7
 VG_TEST_ARGS = --track-origins=yes --leak-check=full --show-reachable=yes --errors-for-leak-kinds=all
@@ -268,16 +270,16 @@ endif
 
 # Keep includes in alpha order.
 check-src-include-order/%: %
-	@if [ "$$(grep '^#include' < $<)" != "$$(grep '^#include' < $< | LC_ALL=C sort)" ]; then echo "$<:1: includes out of order"; grep '^#include' < $<; echo VERSUS; grep '^#include' < $< | LC_ALL=C sort; exit 1; fi
+	@if [ "$$(grep '^#include' < $<)" != "$$(grep '^#include' < $< | $(SORT))" ]; then echo "$<:1: includes out of order"; grep '^#include' < $<; echo VERSUS; grep '^#include' < $< | $(SORT); exit 1; fi
 
 # Keep includes in alpha order, after including "config.h"
 check-hdr-include-order/%: %
 	@if [ "$$(grep '^#include' < $< | head -n1)" != '#include "config.h"' ]; then echo "$<:1: doesn't include config.h first"; exit 1; fi
-	@if [ "$$(grep '^#include' < $< | tail -n +2)" != "$$(grep '^#include' < $< | tail -n +2 | LC_ALL=C sort)" ]; then echo "$<:1: includes out of order"; exit 1; fi
+	@if [ "$$(grep '^#include' < $< | tail -n +2)" != "$$(grep '^#include' < $< | tail -n +2 | $(SORT))" ]; then echo "$<:1: includes out of order"; exit 1; fi
 
 # Make sure Makefile includes all headers.
 check-makefile:
-	@if [ x"$(CCANDIR)/config.h `find $(CCANDIR)/ccan -name '*.h' | grep -v /test/ | LC_ALL=C sort | tr '\n' ' '`" != x"$(CCAN_HEADERS) " ]; then echo CCAN_HEADERS incorrect; exit 1; fi
+	@if [ x"$(CCANDIR)/config.h `find $(CCANDIR)/ccan -name '*.h' | grep -v /test/ | $(SORT) | tr '\n' ' '`" != x"$(CCAN_HEADERS) " ]; then echo CCAN_HEADERS incorrect; exit 1; fi
 
 # Experimental quotes quote the exact version.
 ifeq ($(EXPERIMENTAL_FEATURES),1)
@@ -409,7 +411,7 @@ $(ALL_GEN_HEADERS): ccan/ccan/cdump/tools/cdump-enumstr $(WIRE_GEN) Makefile
 
 update-ccan:
 	mv ccan ccan.old
-	DIR=$$(pwd)/ccan; cd ../ccan && ./tools/create-ccan-tree -a $$DIR `cd $$DIR.old/ccan && find * -name _info | sed s,/_info,, | sort` $(CCAN_NEW)
+	DIR=$$(pwd)/ccan; cd ../ccan && ./tools/create-ccan-tree -a $$DIR `cd $$DIR.old/ccan && find * -name _info | sed s,/_info,, | $(SORT)` $(CCAN_NEW)
 	mkdir -p ccan/tools/configurator
 	cp ../ccan/tools/configurator/configurator.c ../ccan/doc/configurator.1 ccan/tools/configurator/
 	$(MAKE) ccan/config.h