patch type_to_str to handle complex function-ptr decls better

Code like:

    #include <signal.h>
    int main() { _Generic(signal, int: 0); }

should fail with
    error: type 'extern void (*(int, void (*)(int)))(int)' does not match any association
not
    error: type 'extern void *(int)(int, void *(int))' does not match any association

[matz: fix formatting, fix function-to-pointer decay for operands of
_Generic, add testcase for this]

tccgen.c

@@ -19,7 +19,6 @@
  */
 
 #include "tcc.h"
-
 /********************************************************/
 /* global variables */
 
@@ -2938,17 +2937,26 @@ static void type_to_str(char *buf, int buf_size,
         break;
     case VT_FUNC:
         s = type->ref;
-        type_to_str(buf, buf_size, &s->type, varstr);
-        pstrcat(buf, buf_size, "(");
+        buf1[0]=0;
+        if (varstr && '*' == *varstr) {
+            pstrcat(buf1, sizeof(buf1), "(");
+            pstrcat(buf1, sizeof(buf1), varstr);
+            pstrcat(buf1, sizeof(buf1), ")");
+        }
+        pstrcat(buf1, buf_size, "(");
         sa = s->next;
         while (sa != NULL) {
-            type_to_str(buf1, sizeof(buf1), &sa->type, NULL);
-            pstrcat(buf, buf_size, buf1);
+            char buf2[256];
+            type_to_str(buf2, sizeof(buf2), &sa->type, NULL);
+            pstrcat(buf1, sizeof(buf1), buf2);
             sa = sa->next;
             if (sa)
-                pstrcat(buf, buf_size, ", ");
+                pstrcat(buf1, sizeof(buf1), ", ");
         }
-        pstrcat(buf, buf_size, ")");
+        if (s->f.func_type == FUNC_ELLIPSIS)
+            pstrcat(buf1, sizeof(buf1), ", ...");
+        pstrcat(buf1, sizeof(buf1), ")");
+        type_to_str(buf, buf_size, &s->type, buf1);
         goto no_var;
     case VT_PTR:
         s = type->ref;
@@ -5005,6 +5013,8 @@ ST_FUNC void unary(void)
 	skip('(');
 	expr_type(&controlling_type, expr_eq);
 	controlling_type.t &= ~(VT_CONSTANT | VT_VOLATILE | VT_ARRAY);
+	if ((controlling_type.t & VT_BTYPE) == VT_FUNC)
+	  mk_pointer(&controlling_type);
 	for (;;) {
 	    learn = 0;
 	    skip(',');

tests/tests2/94_generic.c

@@ -20,6 +20,12 @@ int b_f()
 	return 10;
 }
 
+typedef int (*fptr)(int);
+int foo(int i)
+{
+  return i;
+}
+
 typedef int int_type1;
 
 #define gen_sw(a) _Generic(a, const char *: 1, default: 8, int: 123);
@@ -60,5 +66,7 @@ int main()
 				long long: "long long"));
 	i = _Generic(l, long: 1, int: 2);
 	printf("%d\n", i);
+	i = _Generic(foo, fptr: 3, int: 4);
+	printf("%d\n", i);
 	return 0;
 }

tests/tests2/94_generic.expect

@@ -10,4 +10,5 @@
 3
 4
 long
-1
+1
+3