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/15.c

@@ -0,0 +1,21 @@
+#define Y(x) Z(x)
+#define X Y
+X(1)
+X(X(1))
+X(X(X(X(X(1)))))
+
+#define A B
+#define B A
+return A + B;
+
+#undef A
+#undef B
+
+#define A B+1
+#define B A
+return A + B;
+
+#define A1 B1+1
+#define B1 C1+2
+#define C1 A1+3
+return A1 + B1;