https://github.com/fanf2/unifdef/pull/13

--- a/tests/multi-generic-sh
+++ b/tests/multi-generic-sh
@@ -9,7 +9,7 @@ unifdef -M~ $opts $mfiles
 e=$?
 for f in $mfiles
 do
-	diff -u $f~ $f | sed '/^[+-]\{3\} /s/	.*//'
+	LANG=C diff -u $f~ $f | sed '/^[+-]\{3\} /s/	.*//'
 	rm -f $f~ $f
 done
 exit $e
--- a/unifdefall.sh
+++ b/unifdefall.sh
@@ -48,7 +48,7 @@ export LC_ALL=C
 # list of all controlling macros; assume these are undefined
 "$unifdef" $debug -s "$@" | sort -u | sed 's/^/#undef /' >"$tmp/undefs"
 # list of all macro definitions
-cc -E -dM "$@" | sort >"$tmp/defs"
+${CC-cc} -E -dM "$@" | sort >"$tmp/defs"
 
 case $debug in
 -d)	cat "$tmp/undefs" "$tmp/defs" 1>&2