tests: g_assert_cmpstr_free() stores the lhs in a temporary variable

Valgrind told me that all calls to g_assert_cmpstr_free() weren't
actually freeing the string.  A closer look shows that if we pass a
function as "lhs" then the function will be called twice, allocating
twice as much memory.

Fix this by storing the result of lhs in a temporary variable so
functions are only ever called once.

Signed-off-by: Anna Schumaker <Anna@NoWheyCreamery.com>

include/tests/test.h

@@ -7,10 +7,16 @@
 #include <glib.h>
 
 
+/*
+ * Compares two strings, and frees lhs before returning.
+ * NOTE: We store lhs in a temporary string so that "lhs" only gets
+ *       evaluated once in the case that it is a function.
+ */
 #define g_assert_cmpstr_free(lhs, cmp, rhs)	\
 do {						\
-	g_assert_cmpstr(lhs, cmp, rhs);		\
-	g_free(lhs);				\
+	gchar *__tmp_str = lhs;			\
+	g_assert_cmpstr(__tmp_str, cmp, rhs);	\
+	g_free(__tmp_str);			\
 } while (0)
 
 #endif /* OCARINA_TESTS_TEST_H */