Merge pull request #1832 from acqn/PPDefineFix

[cc65] Preprocessor directive #define fixes

test/val/bug1822-pptest.c

@@ -0,0 +1,25 @@
+/* Bug #1822 - Redefined macros failed to be all undefined with a single #undef */
+
+#undef F
+#undef F
+
+#define F 1
+#define F 1
+
+#undef F
+#if defined F
+#error #undef F fails!
+#endif
+
+#define F 0
+
+#include <stdio.h>
+
+int main(void)
+{
+    if (F != 0)
+    {
+        printf("failed: F = %d\n", F);
+    }
+    return F;
+}