Add test cases with a question mark

The test framework used to treat them specially (but no longer does). Add
these test cases as non-regression for how the test framework allows "?"
and especially "??" (which I think in the very distant path needed special
handling because the test data was embedded in a .c file, and thus ?? could
be interpreted as the prefix of a trigraph).

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

tests/suites/test_suite_platform_printf.function

@@ -19,6 +19,7 @@
 #define SPACE_CHAR ' '
 #define DOUBLE_QUOTE_CHAR '"'
 #define COLON_CHAR ':'
+#define QUESTION_CHAR '?'
 #define BACKSLASH_CHAR '\\'
 #define LOWERCASE_N_CHAR 'n'
 /* END_HEADER */