tccpp: Fix macro_is_equal

When tokens in macro definitions need cstr_buf inside get_tok_str,
the second might overwrite the first (happens when tokens are
multi-character non-identifiers, see testcase) in macro_is_equal,
failing to diagnose a difference.  Use a real local buffer.

tccpp.c

@@ -1280,17 +1280,18 @@ static int macro_is_equal(const int *a, const int *b)
 {
     CValue cv;
     int t;
+    static CString localbuf;
 
     if (!a || !b)
         return 1;
 
     while (*a && *b) {
-        /* first time preallocate static cstr_buf, next time only reset position to start */
-        cstr_reset(&cstr_buf);
+        /* first time preallocate static localbuf, next time only reset position to start */
+        cstr_reset(&localbuf);
         TOK_GET(&t, &a, &cv);
-        cstr_cat(&cstr_buf, get_tok_str(t, &cv), 0);
+        cstr_cat(&localbuf, get_tok_str(t, &cv), 0);
         TOK_GET(&t, &b, &cv);
-        if (strcmp(cstr_buf.data, get_tok_str(t, &cv)))
+        if (strcmp(localbuf.data, get_tok_str(t, &cv)))
             return 0;
     }
     return !(*a || *b);

tests/pp/16.c

@@ -0,0 +1,3 @@
+/* The following should warn */
+#define A ...
+#define A <<=

tests/pp/16.expect

@@ -0,0 +1,2 @@
+
+16.c:3: warning: A redefined