Fix -Wstring-concatenation warning.

Fix the following clang warning:
gcc/spellcheck.c:477:3: warning: suspicious concatenation of string literals in an array initialization;
did you mean to separate the elements with a comma? [-Wstring-concatenation]

gcc/ChangeLog:

	* spellcheck.c: Add missing comma in initialization.

gcc/spellcheck.c

@@ -473,7 +473,7 @@ static const char * const test_data[] = {
   "foo",
   "food",
   "boo",
-  "1234567890123456789012345678901234567890123456789012345678901234567890"
+  "1234567890123456789012345678901234567890123456789012345678901234567890",
   "abc",
   "ac",
   "ca",