output space after TOK_PPNUM which followed by '+' or '-'

* correct -E output for the case ++ + ++ concatenation
        do this only for expanded from macro string
        and only when tcc_state->output_type == TCC_OUTPUT_PREPROCESS

tests/pp/14.c

@@ -0,0 +1,11 @@
+extern int printf(const char *format, ...);
+#define P ++
+#define n(x) x
+
+int main(void)
+{
+    int a = 0, b = -1;
+    int i1 = a P+P b;
+    printf("i1 = %d\n", i1);
+    return n(0x1e)n(-1);
+}