struct-init: Implement initializing subaggregates

E.g. "struct { struct S s; int a;} = { others, 42 };"
if 'others' is also a 'struct S'.  Also when the value is a
compound literal.  See added testcases.

tests/tests2/86-struct-init.c

@@ -0,0 +1,139 @@
+typedef unsigned char u8;
+typedef struct {} empty_s;
+struct contains_empty {
+    u8 a;
+    empty_s empty;
+    u8 b;
+};
+struct contains_empty ce = { { (1) }, (empty_s){}, 022, };
+/* The following decl of 'q' would demonstrate the TCC bug in init_putv when
+   handling copying compound literals.  (Compound literals
+   aren't acceptable constant initializers in isoc99, but
+   we accept them like gcc, except for this case)
+//char *q = (char *){ "trara" }; */
+struct SS {u8 a[3], b; };
+struct SS sinit16[] = { { 1 }, 2 };
+struct S
+{
+  u8 a,b;
+  u8 c[2];
+};
+
+struct T
+{
+  u8 s[16];
+  u8 a;
+};
+
+struct U
+{
+  u8 a;
+  struct S s;
+  u8 b;
+  struct T t;
+};
+
+struct V
+{
+  struct S s;
+  struct T t;
+  u8 a;
+};
+
+struct W
+{
+  struct V t;
+  struct S s[];
+};
+
+struct S gs = ((struct S){1, 2, 3, 4});
+struct S gs2 = {1, 2, {3, 4}};
+struct T gt = {"hello", 42};
+struct U gu = {3, 5,6,7,8, 4, "huhu", 43};
+struct U gu2 = {3, {5,6,7,8}, 4, {"huhu", 43}};
+/* Optional braces around scalar initializers.  Accepted, but with
+   a warning.  */
+struct U gu3 = { {3}, {5,6,7,8,}, 4, {"huhu", 43}};
+/* Many superfluous braces and leaving out one initializer for U.s.c[1] */
+struct U gu4 = { 3, {5,6,7,},  5, { "bla", {44}} };
+/* Superfluous braces and useless parens around values */
+struct S gs3 = { (1), {(2)}, {(((3))), {4}}};
+/* Superfluous braces, and leaving out braces for V.t, plus cast */
+struct V gv = {{{3},4,{5,6}}, "haha", (u8)45, 46};
+/* Compund literal */
+struct V gv2 = {(struct S){7,8,{9,10}}, {"hihi", 47}, 48};
+/* Parens around compound literal */
+struct V gv3 = {((struct S){7,8,{9,10}}), {"hoho", 49}, 50};
+/* Initialization of a flex array member (warns in GCC) */
+struct W gw = {{1,2,3,4}, {1,2,3,4,5}};
+
+#include <stdio.h>
+void print_ (const char *name, const u8 *p, long size)
+{
+  printf ("%s:", name);
+  while (size--) {
+      printf (" %x", *p++);
+  }
+  printf ("\n");
+}
+#define print(x) print_(#x, (u8*)&x, sizeof (x))
+#if 1
+void foo (struct W *w)
+{
+  struct S ls = {1, 2, 3, 4};
+  struct S ls2 = {1, 2, {3, 4}};
+  struct T lt = {"hello", 42};
+  struct U lu = {3, 5,6,7,8, 4, "huhu", 43};
+  struct U lu1 = {3, ls, 4, {"huhu", 43}};
+  struct U lu2 = {3, (ls), 4, {"huhu", 43}};
+  /* Incomplete bracing.  */
+  struct U lu21 = {3, ls, 4, "huhu", 43};
+  /* Optional braces around scalar initializers.  Accepted, but with
+     a warning.  */
+  struct U lu3 = { 3, {5,6,7,8,}, 4, {"huhu", 43}};
+  /* Many superfluous braces and leaving out one initializer for U.s.c[1] */
+  struct U lu4 = { 3, {5,6,7,},  5, { "bla", 44} };
+  /* Superfluous braces and useless parens around values */
+  struct S ls3 = { (1), (2), {(((3))), 4}};
+  /* Superfluous braces, and leaving out braces for V.t, plus cast */
+  struct V lv = {{3,4,{5,6}}, "haha", (u8)45, 46};
+  /* Compund literal */
+  struct V lv2 = {(struct S)w->t.s, {"hihi", 47}, 48};
+  /* Parens around compound literal */
+  struct V lv3 = {((struct S){7,8,{9,10}}), w->t.t, 50};
+  print(ls);
+  print(ls2);
+  print(lt);
+  print(lu);
+  print(lu1);
+  print(lu2);
+  print(lu21);
+  print(lu3);
+  print(lu4);
+  print(ls3);
+  print(lv);
+  print(lv2);
+  print(lv3);
+}
+#endif
+
+int main()
+{
+  print(ce);
+  print(gs);
+  print(gs2);
+  print(gt);
+  print(gu);
+  print(gu2);
+  print(gu3);
+  print(gu4);
+  print(gs3);
+  print(gv);
+  print(gv2);
+  print(gv3);
+  print(sinit16);
+  print(gw);
+  foo(&gw);
+  //printf("q: %s\n", q);
+  return 0;
+}